Process for preparing and crosslinking a cable comprising a polymer composition and a crosslinked cable

ABSTRACT

The application relates to a process for preparing a crosslinked cable, including: —applying one or more layers including a polymer composition on a conductor, wherein at least one layer includes one or more free radical generating agents, —crosslinking by radical reaction said at least one layer including said free radical generating agent(s), —cooling the obtained crosslinked cable in pressurized conditions, and —reducing or removing the content of volatile decomposition products(s), which are originating from optionally in elevated temperature, from the crosslinked cable obtained from cooling and recovery step.

FIELD OF INVENTION

The invention relates to a process for preparing a cable or wire using aradical generating agent, as well as to a crosslinked cable or wire. Theinvention also relates to a polymer composition usable in a cable layer,to preparation process thereof and to free radical generating agents forcrosslinking by radical reaction.

BACKGROUND ART

It is known to use free radical generating agents for modifying aproduct, such as a polymer composition via a radical reaction.

Free radical agents are used e.g. to initiate (a) crosslinking in apolymer, i.a. primarily formation of interpolymer crosslinks (bridges)by radical reaction, (b) grafting in a polymer, i.e. introduction ofcompounds to a polymer chain (to backbone and/or side chains) by radicalreaction, and (c) visbreaking in a polymer, i.e. modification of meltflow rate (MFR) of a polymer by radical reaction. These polymermodifications are well known in the art.

When added to a polymer composition, free radical generating agents actby generating radicals, typically by decomposing to radicals, underconditions which enable the radical formation. The decomposed radicalsinitiate further radical reactions within a polymer composition. Theresulting decomposition products of the free radical generating agentare typically a result of several reactions of the decompositionproducts of initial radical forming reaction. Said resultingdecomposition products typically remain in the modified polymer and mayinclude detrimental, undesired decomposition products.

Peroxides are very common free radical generating agents used i.a. inthe polymer industry for said polymer modifications. The resultingdecomposition products of peroxides may include volatile by-products.For example, dicumylperoxide, which is commonly used peroxide in polymerfield, decomposes i.a. to methane, acetophenone and cumylalcohol duringthe radical formation step, e.g. during a crosslinking step. The formedgaseous methane (CH₄) is flammable, explosive and volatile and thus arisk in a working environment.

In wire and cable applications, a typical cable comprises at least oneconductor surrounded by one or more layers of polymeric materials. Insome power cables, including medium voltage (MV), high voltage (HV) andextra high voltage (EHV) cables, said conductor is surrounded by severallayers including an inner semiconductive layer, an insulation layer andan outer semiconductive layer, in that order. The cables are commonlyproduced by extruding the layers on a conductor. One or more of saidlayers are then typically crosslinked to improve i.a. deformationresistance at elevated temperatures, as well as mechanical strengthand/or chemical resistance, of the layer(s) of the cable. The freeradical generating agent, such as peroxide, is typically incorporatedinto the layer material prior to the extrusion of the layer(s) on aconductor. After formation of the layered cable, the cable is thensubjected to a crosslinking step to initiate the radical formation andthereby crosslinking reaction.

The decomposition products of the free radical forming agent remainmostly captured within the cable layer after crosslinking. This causesproblems in view of the cable manufacturing process as well as in viewof the quality of the final cable.

Accordingly, after crosslinking the cable must be cooled with great careto prevent the gaseous volatile decomposition products like methaneforming voids within the polymer layer. These voids have typically anaverage diameter of between 10 to 100 μm. Partial discharges can takeplace in such voids within a cable that is subjected to an electricalfield and thereby reduce the electrical strength of the cable.

The MV, HV and EHV power cables must have high layer quality in terms ofsafety during installation and in end use thereof. In service, volatiledecomposition products in a cable resulting from a crosslinking step cancreate a gas pressure and thus cause defects in the shielding and in thejoints. E.g. when a cable is equipped with a metal barrier, then thegaseous products can exert a pressure, especially on the joints andterminations, whereby a system failure may occur.

For the above reasons the volatile decomposition products, such asmethane e.g. where dicumylperoxide is used, are conventionally reducedto a minimum or removed after crosslinking and cooling step. Such aremoval step is generally known as a degassing step.

The degassing step is time and energy consuming and is thus a costlyoperation in a cable manufacturing process. Degassing requires largeheated chambers which must be well ventilated to avoid the build-up ofe.g. flammable methane and ethane. The cable, typically wound on tocable drums, is normally degassed at elevated temperature in the rangeof 50-80° C., e.g. 60-70° C., for lengthy time periods. At thesetemperatures however, thermal expansion and softening of the insulationcan occur and lead to undue deformation of the formed cable layersresulting directly in failures of the cable. The degassing of MV, HV andEHV cables with high cable weight needs thus often be carried out atdecreased temperatures.

Accordingly, there is a need to find new solutions to overcome the priorart problems.

OBJECTS OF THE INVENTION

An object of the invention is to provide a process for producing and aprocess for crosslinking a cable, which process enables the preparationof high quality products with shorter overall production time and/orlower energy consumption.

Another object of the invention is to provide a crosslinked cable whichcomprises one or more layers comprising a crosslinked polymercomposition, which cable has highly advantageous properties, such as ahigh quality and superior processability properties.

The invention and further objects thereof are described and defined indetails below.

DESCRIPTION OF THE INVENTION

As to the first object, the invention is directed to a process forpreparing a crosslinked cable, comprising i.a. the steps of:

-   -   applying one or more layers comprising a polymer composition on        a conductor, wherein at least one layer comprises one or more        free radical generating agents,    -   crosslinking by radical reaction said at least one layer        comprising said free radical generating agent(s),    -   cooling the obtained crosslinked cable under pressurized        conditions, and    -   reducing or removing the content of volatile decomposition        products(s), at ambient or in elevated temperature, from said        crosslinked cable obtained from said cooling step;    -   characterized in that said process comprises one or two of the        following features:    -   said reduction or removal step is carried out in more than 50%        shorter period of time than the time period required for a        reference cable which is a crosslinked and cooled cable having        the same structure and layer material in each of said one or        more layers, and prepared using the same process steps and        conditions thereof, as well as the same degree of crosslinking,        as said claimed crosslinked and cooled cable, but using a        dicumyl peroxide as the free radical generating agent, in order        for said reference cable to obtain the same content of said        volatile decomposition product(s) as said claimed cable by using        the same reduction or removal conditions as said claimed cable,        or    -   said reduction or removal step is carried out in a lower        temperature than the temperature required for a reference cable        which is a crosslinked and cooled cable having the same        structure and layer material in each of said one or more layers,        and prepared using the same process steps and conditions        thereof, as well as the same degree of crosslinking, as said        claimed crosslinked and cooled cable, but using a dicumyl        peroxide as the free radical generating agent,        in order for said reference cable to obtain the same content of        said volatile decomposition product(s) as said claimed cable.

Said crosslinked and cooled cable which is crosslinked using dicumylperoxide and used above and in claim 1 for the comparison of thereduction/removal step is abbreviated herein as “crosslinked referencecable”.

The “reduction or removing step” is referred herein below as degassingstep. The “same reduction or removal conditions” mean preferably thesame temperature and ventilation. Conditions are not critical and dependi.a. on the type and size of the cable. Essential for said comparisonsis that the chosen conditions are the same. The term “volatiledecomposition products” are decomposition products formed during thecrosslinking, and possibly during the cooling step, by initiation of thefree radical generating agent as further defined and explained below.E.g. methane and ethane are such volatiles. Preferably, said volatiledecomposition products are compounds having boiling point at atmosphericpressure below 50° C., preferably below 80° C. more preferably below100° C. The same volatile decomposition product(s) are used for thecomparison, e.g. methane produced. The “degree of crosslinking” can bemeasured using any crosslinking determination, for example using wellknown so called hot set or gel content determination.

Preferably, in said crosslinking process of the invention, saiddegassing step is carried out in more than 70%, preferably in more than90%, shorter period of time than the degassing step of the crosslinkedand cooled reference cable as defined above and in claim 1. In onepreferable embodiment the crosslinking method of the invention saiddegassing step can be completely avoided with the crosslinking processof the invention. In a further embodiment, during the crosslinking andcooling step of the invention no detectable methane is formed whenmeasured as defined below under “GC-analysis protocol” is formed andthus the crosslinking method may be made without a degassing step. Thensaid difference in time is naturally 100% compared to crosslinked andcooled reference cable.

Thus, viewed from another aspect the invention provides a process forpreparing a crosslinked cable, comprising the steps of:

-   -   (i) applying one or more layers comprising a polymer composition        on a conductor, wherein at least one layer comprises one or more        free radical generating agents,    -   (ii) crosslinking by radical reaction said at least one layer        comprising said free radical generating agent(s),    -   (iii) cooling the obtained crosslinked cable under pressurized        conditions, and    -   (iv) using the product of step (iii) as a cable (i.e. no        degassing step takes place).

Viewed from another aspect the invention provides a process forpreparing a crosslinked cable, comprising the steps of:

-   -   (i) applying one or more layers comprising a polymer composition        on a conductor, wherein at least one layer comprises one or more        free radical generating agents,    -   (ii) crosslinking by radical reaction said at least one layer        comprising said free radical generating agent(s),    -   (iii) cooling the obtained crosslinked cable under pressurized        conditions, and    -   (iv) reducing or removing the content of volatile decomposition        products(s), at ambient or in elevated temperature, from said        crosslinked cable obtained from said cooling step; wherein said        one or more free radical generating agents is a compound of        formula (I) as herein described.

The preferable conditions of the crosslinking, cooling and degassingstep of the process of the invention, as well as other features of theinvention and preferable embodiments, variants and subgroups thereof arefurther specified below.

Compounds of the Invention

The below defined compounds are preferable free radical generatingagents for use in the present process as defined above and in belowclaims. Moreover said compounds as such form an independent invention.

Accordingly, in a first embodiment, the invention provides a compoundfor use as a free radical generating agent which compound results inmethane (CH₄) content of less than 300 ppm (weight), preferably of lessthan 200 ppm (weight), preferably of less than 100 ppm (weight) morepreferably of 0 to 50 ppm (weight), as a decomposition product thereof.

Generally, in above and below definitions the given values in ppm formethane and/or other volatile content are determined by gaschromatography from the obtained crosslinked polymer composition as suchor from a crosslinked cable layer, depending on the definition,according to a method as described below under “GC-analysis protocol”.Accordingly, the produced methane or other volatile content can equallybe determined from a crosslinked polymer composition as such or from acrosslinked manufactured article thereof, as desired, each consisting ofthe polymer composition of the invention. The sample under the test iscrosslinked using the test free radical generating agent in such anamount which results in a crosslinking degree expressed as gel contentof 50%, and preferably gel content of at least 50%. The gel content (%)is measured according to ASTM D2765-01 Method A or B (depending on thenature of the sample). Such a crosslinked sample is then used forpreparing the sample for volatile content measurement of GC-analysisprotocol.

Without limiting to any theory, the terms “a decomposition product(s)thereof” or “a decomposition product of a free radical generating step”etc. as used above and below mean herein a by-product(s) formed during afree radical generating step, e.g. crosslinking step, and possibly alsoduring the cooling step, by initiation of the free radical generatingagent, as well known in the art. As an example methane may be onedecomposition product which is an undesired decomposition product of theinvention. Further decomposition products are specified below, which maynot be desired in various embodiments of the invention.

Alternatively, the compound of the invention can also be defined as acompound for use as a free radical generating agent which in said useresults in CH₄ content of less than 300 ppm (weight), preferably of lessthan 200 ppm (weight), preferably of less than 100 ppm (weight), morepreferably of 0 to 50 ppm (weight), even more preferably is withoutresulting in CH₄, as a decomposition product thereof.

The invention, in a second embodiment, is also directed independently toa compound for use as a free radical generating agent which compound iswithout CH₄ as a decomposition product thereof. The absence of methanecan be determined according to a method described below under“GC-analysis protocol”.

Said first and second groups of the compound of the invention areunitary and all alternatives define the principal of the presentinvention in terms of residues originating from a free radicalgenerating agent.

The term “without resulting in CH₄ as a decomposition product thereof”means that a compound of the present invention generates no methane, orin alternative terms does not decompose to the undesired volatile CH₄by-product during a radical formation step in an industrial process.

The solution of the invention provides a new principal which issurprising and unobvious, since in the prior art there is no teaching orany indication to modify the free radical generating agent in order toavoid formation of CH₄ as a decomposing product during the free radicalformation step in an industrial process. For example, in crosslinkingapplications, the prior art has proposed merely solutions relating tobalance the amount of free radical generating agent and the neededdegree of crosslinking.

Thus the invention further provides an industrial process, whichcomprises a step of forming free radicals using a free radicalgenerating agent suitable for modifying a product via radical reaction,wherein a free radical generating compound is used which results in CH₄content of less than 300 ppm (weight), preferably of less than 200 ppm(weight), preferably of less than 100 ppm (weight), more preferably of 0to 50 ppm (weight), even more preferably is without resulting to CH₄, asa decomposition product thereof.

In one embodiment said compound of the invention results in reducedamount of or preferably does not decompose to low molecular weightcompounds selected from (C1-C3)alkanes when generating free radicals,e.g. in industrial applications.

In another embodiment of the invention it is advantageous that saidcompound as a free radical generating agent results in reduced amount ofor preferably is without (C1-C4)alkanes as decomposition productsthereof when generating free radicals, e.g. in industrial applications.

In embodiments, wherein very high quality is required for the productsmodified by using a free radical agent, then it is preferable that saidcompound results in reduced amount of or is preferably without(C1-C6)alkanes as decomposition products thereof during a free radicalforming step, e.g. in an industrial process.

The term “a free radical generating agent” is defined herein above orbelow to be any compound capable of generating radicals, e.g. inindustrial applications, e.g. which can initiate a modification reactionin a polymer, such as a crosslinking, grafting or visbreaking reactionin a polymer.

As a further independent invention, the invention is directed to acompound for use as a free radical generating agent which bears one ormore moieties in its structure which are decomposable to a decompositionproduct in a free radical generating step, characterized in that saidcompound is selected from one or more of:

-   -   a compound, wherein said one or more decomposable moieties        result in a CH₄ content of less than 300 ppm (weight),        preferably of less than 200 ppm (weight), preferably of less        than 100 ppm (weight), more preferably of up to 50 ppm (weight)        as said decomposition product; or    -   a compound without any such moiety that is decomposable to CH₄        as said decomposition product; or any mixture thereof.

Preferably, said compound of the invention contains at least one —O—O—bond or at least one —N═N— bond. More preferably, said compound of theinvention is a peroxide, preferably an organic peroxide compound.

The compounds of the invention as defined above by a feature of thedecomposition product thereof form an independent first and secondgroups of the compounds of invention.

A third independent invention is directed to a compound for use as afree radical generating agent which does not result in (i.e. is without)decomposition products, preferably hydrocarbon decomposition products,having a boiling point at atmospheric pressure of less than 50° C.,preferably less than 80° C., or in some embodiments even less than 100°C. may be desired. “Hydrocarbon” has the same meaning as given below for“hydrocarbyl” which represents a hydrocarbon as a monovalentsubstituent. Preferably, this 3^(rd) group of compounds of the inventionand the above first and second groups of compounds of invention can bedependent on each other, in any order.

The invention is further independently directed to a compound for use asa free radical generating agent which is an organic peroxide of formula(I)

wherein

-   -   R¹ and R^(1′) are each independently H, substituted or        unsubstituted saturated or partially unsaturated hydrocarbyl or        substituted or unsubstituted aromatic hydrocarbyl;        -   wherein each of said substituted or unsubstituted saturated            or partially unsaturated hydrocarbyl or aromatic hydrocarbyl            optionally comprises one or more heteroatoms;        -   wherein said substituted or unsubstituted saturated or            partially unsaturated hydrocarbyl include, preferably is            selected from, (i) straight or branched chain saturated or            partially unsaturated hydrocarbyls, (ii) straight or            branched chain saturated or partially unsaturated            hydrocarbyls which bear saturated or partially unsaturated            cyclic hydrocarbyl and (iii) saturated or partially            unsaturated cyclic hydrocarbyls;        -   wherein each of said aromatic hydrocarbyl and said saturated            or partially unsaturated cyclic hydrocarbyl is independently            a monocyclic or multicyclic ring system; and        -   wherein said substituted saturated or partially unsaturated            hydrocarbyl or substituted aromatic hydrocarbyl comprise            independently 1 to 4 substituents selected from a functional            group, a saturated or partially unsaturated hydrocarbyl            optionally bearing a functional group or aromatic            hydrocarbyl optionally bearing a functional group;    -   R², R²′, R³ and R³′ are each independently H, substituted or        unsubstituted saturated or partially unsaturated hydrocarbyl or        substituted or unsubstituted aromatic hydrocarbyl;        -   wherein each of said substituted or unsubstituted saturated            or partially unsaturated hydrocarbyl or aromatic hydrocarbyl            optionally comprises one or more heteroatoms;        -   wherein said substituted or unsubstituted saturated or            partially unsaturated hydrocarbyl include (i) straight or            branched chain saturated or partially unsaturated            hydrocarbyls, (ii) straight or branched chain saturated or            partially unsaturated hydrocarbyls which bear saturated or            partially unsaturated cyclic hydrocarbyl and (iii) saturated            or partially unsaturated cyclic hydrocarbyls;        -   wherein each of said aromatic hydrocarbyl and said saturated            or partially unsaturated cyclic hydrocarbyl is independently            a monocyclic or multicyclic ring system; and        -   wherein said substituted saturated or partially unsaturated            hydrocarbyl or substituted aromatic hydrocarbyl comprise            independently 1 to 4 substituents selected from a functional            group or a saturated or partially unsaturated hydrocarbyl            optionally bearing a functional group or aromatic            hydrocarbyl optionally bearing a functional group; or    -   R² and R³ together with the carbon atom (C¹) to which they are        attached form an unsubstituted or substituted saturated or        partially unsaturated carbocyclic ring moiety of 3 to 14        C-atoms, preferably 5-12 C atoms; an unsubstituted or        substituted saturated or partially unsaturated heteroring moiety        of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4        heteroatoms, selected from O, N, P, S or Si; or an unsubstituted        or substituted aromatic ring moiety of 3 to 14 C-atoms,        preferably of 5-12 C atoms, optionally comprising 1 to 4        heteroatoms;        -   wherein said carbocyclic ring, heteroring or aromatic ring            system is optionally fused with another optionally            substituted ring system having 4 to 14 ring atoms; and        -   wherein said substituted carbocyclic ring, heteroring or            aromatic ring system comprises 1 to 4 substituents selected            independently from a functional group, or a saturated or            partially unsaturated hydrocarbyl optionally bearing a            functional group, or aromatic hydrocarbyl optionally bearing            a functional group; or    -   R²′ and R³′ together with the carbon atom (C¹′) to which they        are attached form an unsubstituted or substituted saturated or        partially unsaturated carbocyclic ring moiety of 3 to 14        C-atoms, preferably of 5-12 C atoms; an unsubstituted or        substituted saturated or partially unsaturated heteroring moiety        of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4        heteroatoms, selected from O, N, P, S or Si; or unsubstituted or        substituted aromatic ring moiety of 3 to 14 C-atoms, preferably        moiety of 5 to 12 C atoms; optionally comprising 1 to 4        heteroatoms;        -   wherein said carbocyclic ring, heteroring or aromatic ring            system is optionally fused with another optionally            substituted ring system having 4 to 14 ring atoms; and        -   wherein said substituted carbocyclic ring, heteroring or            aromatic ring system comprises 1 to 4 substituents selected            independently from a functional group or a saturated or            partially unsaturated hydrocarbyl optionally bearing a            functional group or aromatic hydrocarbyl optionally bearing            a functional group; or    -   R² and R²′ form together a bivalent substituted or unsubstituted        saturated or partly unsaturated hydrocarbyl optionally        containing 1 to 4 heteroatoms, wherein R² is linked to C¹ and        R²′ to C¹′, respectively, forming together with C¹—O—O—C¹′— a        substituted or unsubstituted saturated or partially unsaturated        carbocyclic ring moiety of 3 to 14 C-atoms, preferably moiety of        5-12 C atoms, comprising optionally, in addition to said at        least two O atoms, 1 to 4 further heteroatoms; wherein said        carbocyclic ring or heteroring system is optionally fused with        another ring system having 4-14 ring atoms;        and functional derivatives thereof;    -   with the proviso that at least two of R¹, R² and R³, and at        least two of R¹′, R²′ and R³′, respectively, are other than H or        methyl.    -   Preferably, the compound of formula (I) is other than        diphenylcyclohexyl peroxide.

U.S. Pat. No. 3,079,370 discloses a generic group of peroxides, butwithout specifying any peroxides with less than two methyls at carbonatoms corresponding C¹ and C^(1′) in formula (I) above.

In a preferred embodiment, the compounds of the invention are subject tothe third proviso that when R² and R³ together with the carbon atom (C¹)to which they are attached form a carbocyclic ring moiety of 3 to 14C-atoms as defined above, and R²′ and R³′ together with the carbon atom(C¹′) to which they are attached form the carbocyclic ring moiety of 3to 14 C-atoms as defined above, then R¹ or R¹′ cannot be anunsubstituted aromatic hydrocarbyl.

It will be appreciated that whilst some peroxides are known per se theyhave not been disclosed in connection with polymer modification, inparticular specific types of polymer modification and especially incable cross-linking. The above second and third provisos are nottherefore essential (although may be preferred) where the inventionconcerns modified polymer compositions and cables made therefrom.

The compounds of formula (I):

-   -   form a fourth independent group of compounds of the invention        but all groups have the same unitary feature, i.e. a reduced        amount of a volatile decomposition products compared to the        prior art. All four groups of compounds of the invention can be        made dependent on each other in any combination, and in any        order.

Preferably, the compound of formula (I) as defined above results in CH₄content of less than 300 ppm (weight), preferably of less than 200 ppm(weight), preferably less than 100 ppm (weight), more preferably iswithout CH₄ as a decomposition product thereof, during an industrialprocess for generating free radicals, e.g. during a modification step ofa polymer composition.

The terms used for defining the compounds of formula (I) are well knownin the organic chemistry. E.g. in moieties defined in formula (I):

When the substituents are defined herein as “hydrocarbyl”, “aromatichydrocarbyl”, “alkyl” etc. it is evident that they mean “a hydrocarbylgroup”, “an alkyl group” etc. For the avoidance of doubt, the term“hydrocarbyl” used herein does not encompass aromatic groups as is clearfrom the definitions used herein. The substituents are referred hereininterchangeably as “radical” or “group”, as known in the field.

Any hydrocarbyl group of the invention will preferably have up to 40 C,atoms, preferably up to 30 C atoms, e.g. up to 20 C atoms, especially upto 12 carbon atoms. Some highly preferred hydrocarbyls may have 1 to 6carbon atoms.

Alkyl groups, alkenyl groups or alkynyl groups defined in formula (I)and (V) and in preferable embodiments, and subgroups thereof as definedabove below and claims, will preferably have up to 40 C, atoms,preferably up to 30 C atoms, e.g. up to 20 C atoms. Some highlypreferred alkyl groups may have 1 to 12 carbon atoms, more preferablymay be methyl or have 6 to 12 carbon atoms.

Cyclic alkyl or cyclic alkenyl groups will preferably having up to 20 Catoms, especially up to 12 carbon atoms. Some highly preferred cyclicalkyl groups may have 3 to 8 carbon atoms. Preferred cyclic alkenylgroups may have 5 to 8 carbon atoms.

Aromatic hydrocarbyl groups may have up to 40 C, atoms, preferably up to30 C atoms, e.g. up to 20 C atoms, especially up to 12 carbon atoms.Some highly preferred aromatic hydrocarbyls may have 6 to 12 carbonatoms.

The expression “partially unsaturated” means that the moiety maycomprise one or more double or triple bonds and include alkenyl radicalscomprising at least one double bond and alkynyl radicals comprising atleast one triple bond. In case of “partially unsaturated cyclichydrocarbyl” there can be one or more double bonds in the ring systemsmeaning that the ring is non-aromatic to differentiate said “partiallyunsaturated” ring moieties from “aromatic rings” such as phenyl orpyridyl radicals.

“Hetero atoms” present in the moieties of the invention are selectedfrom N, O, P, S or Si. Such moieties include e.g. hydrocarbyl or cyclichydrocarbyl moieties containing one or more heteroatoms, as definedabove and below, and to heteroring or heterocyclic ring moieties asdefined above and below, which are understood to contain C-atoms inaddition to the heteroatoms.

The expression “monocyclic” includes monocyclic ring systems, such ascyclopentyl, cyclohexyl, cycloheptyl or phenyl.

The expression “multicyclic” in turn means herein fused ring systems,such as naphthyl.

Unless otherwise defined herein, the term “carbocyclic” meanssubstituted or unsubstituted saturated or partially unsaturated cyclichydrocarbyl ring system; or substituted or unsubstituted aromatichydrocarbyl ring system.

The term “functional group” as a substituent is well known expressionand includes i.a. —OH, —NR₂, wherein each R is independently H or(C1-C12)alkyl; COR″, wherein R″ is i.a. H, (C1-C12)alkyl or —NR₂,wherein each R is as defined for —NR₂; COOR″, wherein R″ is as definedfor —COR″. A further functional group is a halogen, such as —F, —Cl or—I.

Other preferred functional groups include alkoxy, e.g. OC₁₋₁₂alkyl,nitro, thiol, thioC₁₋₁₂alkyl and CN.

The term “optional” means “may or may not be present”, e.g. “optionallysubstituted” cover the possibilities that a substituent is present andor not present. The term “unsubstituted” naturally means that nosubstituent is present.

When R² and R³ together with C¹ to which they are attached form a ringsystem as defined above, or respectively, R^(2′) and R^(3′) togetherwith C^(1′) to which they are attached form a ring system as definedabove, then, as C¹/C^(1′) are fully valenced, it is understood hereinthat any optional substituents or substituent(s) Z as used above andbelow means substituents linked to ring atom(s) other than C¹ andC^(1′), respectively.

In compounds (I), when R² and R³ form together with C¹ an aromatic ringas defined above, then R¹ is not present, and, respectively, when R²′and R³′ form together with C¹′ an aromatic ring, as defined above, thenR¹′ is not present. Preferably however R² and R³ together with C¹ andR²′ and R³′ together with C¹′ do not form an aromatic ring.

By functional derivative of compounds of formula (I) means that at leastone of R¹, R², R³, R¹′, R²′, R³′ is in form of functional derivative.The term “functional derivative” includes i.a. esters and salts ofcompounds of formula (I), in particular esters and salts of substituentsR¹, R², R³, R¹′, R²′, R³′. Preferred compounds (I) are those, whereinR¹, R², R³, R¹′, R²′, R³′ are as defined above or below are notfunctional derivatives thereof.

A further preferred subgroup of compounds of formula (I) is a compoundof formula (V)

wherein the compounds are selected from any of the alternatives (i) to(iii):

-   (i) R¹ and R^(1′) are each independently H, substituted or    unsubstituted saturated or partially unsaturated hydrocarbyl;    -   wherein each of said substituted or unsubstituted saturated or        partially unsaturated hydrocarbyl optionally comprises one or        more heteroatoms;    -   wherein said substituted or unsubstituted saturated or partially        unsaturated hydrocarbyl include (i) straight or branched chain        saturated or partially unsaturated hydrocarbyls, (ii) straight        or branched chain saturated or partially unsaturated        hydrocarbyls which bear saturated or partially unsaturated        cyclic hydrocarbyl and (iii) saturated or partially unsaturated        cyclic hydrocarbyls;    -   wherein each of said saturated or partially unsaturated cyclic        hydrocarbyl is independently a monocyclic or multicyclic ring        system; and    -   wherein said substituted saturated or partially unsaturated        hydrocarbyl comprise independently 1 to 4 substituents selected        from a functional group, a saturated or partially unsaturated        hydrocarbyl optionally bearing a functional group or aromatic        hydrocarbyl optionally bearing a functional group; and    -   R², R²′, R³ and R³′ are each independently as defined above for        R¹ and R¹′;        or-   (ii) R¹ and R¹′ are each independently an optionally substituted,    preferably unsubstituted, monocyclic (C5-C7)aryl, preferably phenyl,    -   wherein said substituted monocyclic (C5-C7)aryl comprises        independently 1 to 4 substituents selected from a functional        group, a saturated or partially unsaturated hydrocarbyl        optionally bearing a functional group or aromatic hydrocarbyl        optionally bearing a functional group; and-   R² and R²′ are same and are both methyl; and-   R³ and R³′ are each independently H, substituted or unsubstituted    saturated or partially unsaturated hydrocarbyl as defined above    under (i) for R¹ and R^(1′); or-   (iii)-   R¹ and R¹′ are each independently H, substituted or unsubstituted    saturated or partially unsaturated hydrocarbyl as defined above    under (i) for R¹ and R^(1′); and    -   R² and R³ together with the carbon atom (C¹) to which they are        attached form an unsubstituted or substituted saturated or        partially unsaturated carbocyclic ring moiety of 3 to 14        C-atoms, preferably 5-12 C atoms; or an unsubstituted or        substituted saturated or partially unsaturated heteroring moiety        of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4        heteroatoms, selected from O, N, P, S or Si;        -   wherein said carbocyclic ring or heteroring is optionally            fused with another optionally substituted ring system having            4 to 14 ring atoms; and        -   wherein said substituted carbocyclic ring or heteroring            system comprises 1 to 4 substituents selected independently            from a functional group, or a saturated or partially            unsaturated hydrocarbyl optionally bearing a functional            group; and    -   R²′ and R³′ together with the carbon atom (C¹′) to which they        are attached form an unsubstituted or substituted saturated or        partially unsaturated carbocyclic ring moiety of 3 to 14        C-atoms, preferably of 5-12 C atoms; an unsubstituted or        substituted saturated or partially unsaturated heteroring moiety        of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4        heteroatoms, selected from O, N, P, S or Si;        -   wherein said carbocyclic ring or heteroring system is            optionally fused with another optionally substituted ring            system having 4 to 14 ring atoms; and        -   wherein said substituted carbocyclic ring or heteroring            system comprises 1 to 4 substituents selected independently            from a functional group or a saturated or partially            unsaturated hydrocarbyl optionally bearing a functional            group;    -   with a proviso for alternatives (i) to (iii) that at least two        of R¹, R² and R³, and at least two of R¹′, R²′ and R³′,        respectively, are other than H or methyl.

The compounds of formula (V) are preferably selected from thealternatives (ii) or (iii), more preferably from alternative (iii).

The substituents R¹, R², R³, R¹′, R²′ and R³ of compounds of formula (I)or (V) may each independently optionally carry 1 to 4 substituents asdefined above. Said optional substituents may preferably be selectedeach independently from a functional group as defined above; saturatedor partially unsaturated hydrocarbyl optionally bearing a functionalgroup; or aromatic hydrocarbyl optionally bearing a functional group, asdefined above, preferably from C1-12 hydrocarbyl (e.g. C1-6 alkyl) orfrom a functional groups as defined above. If a substituent is present,preferably 1 substituent is present.

Preferred aspects discussed above and below with respect to formula (I)also apply to compounds of formula (V).

The following subgroups of the compound of formula (I) of the inventionrepresent some preferable embodiments and variants of the invention. Itis also understood that said below subgroups further specify thesubstituents given above in formula (I). Each subgroups definition canbe combined with any other subgroup to define further preferredsubgroups within the broadest scope of compounds of formula (I) of theinvention.

Moreover said above generally defined compounds of first, second andthird group and said subgroups thereof, and the general definition forcompounds of formula (I), as well as said subgroups thereof, can becombined in any combination in their uses for modifying polymers, tomodification methods, to modified polymers and to articles comprisingsaid modified polymers, as well as to preparation process thereof, whichall aspects of the invention are discussed below.

In a preferred embodiment of the invention compounds of formula (I) aresymmetrical.

A first preferable embodiment (A) comprises a subgroup (1) of thecompound of formula (I) as defined above, wherein R² and R³ togetherwith carbon atom (C¹) to which they are attached form an optionallysubstituted carbocyclic ring moiety of 3 to 12 ring C-atoms or anoptionally substituted heteroring moiety of 3 to 12 ring atomscontaining 1 to 6, preferably 1 to 4, heteroatoms selected from O, N, P,S or Si, and wherein said carbocyclic or heterocyclic ring system isoptionally fused with another ring system having 4 to 14 ring atoms.This optionally fused ring system may also carry substituents, e.g. 1 to4 groups Z as herein defined or may be unsubstituted.

Preferably R² and R³ together with carbon atom (C¹) form a (C3-C12)carbocyclic ring moiety. The (C3-C12) carbocyclic ring moiety mayoptionally be substituted with 1 to 4 substituents which are preferablyselected from substituents (Z) as defined later below.

In a subgroup (2) of the compound of formula (I) as defined above, R²′and R³′ together with carbon atom (C1′) to which they are attached forman optionally substituted carbocyclic ring moiety of 3 to 12 ringC-atoms or an optionally substituted heteroring moiety of 3 to 12 ringatoms containing 1 to 6, preferably 1 to 4, heteroatoms selected from O,N, P, S or Si, and wherein said carbocyclic or heterocyclic ring systemis optionally fused with another ring system having 4 to 14 ring atoms.This optionally fused ring system may also carry substituents e.g. 1 to4 groups Z as herein defined or may be unsubstituted

Preferably R²′ and R³′ together with carbon atom (C¹′) form a (C3-C12)carbocyclic ring moiety. Said (C3-C12) carbocyclic ring moiety mayoptionally be substituted with 1 to 4 substituents which are preferablyselected from substituents (Z) as defined later below.

In a subgroup (3) of the compound of formula (I) as defined above, R²and R³ together with the carbon atom (C¹) to which they are attachedform an optionally substituted, saturated or partially unsaturated mono-or bicyclic (C4-C14) carbocyclic ring, preferably unsubstitutedsaturated monocyclic (C5-C8) carbocyclic ring, such as cyclopentyl,cyclohexyl or cycloheptyl, preferably cyclohexyl or cyclopentyl. Alsopreferably, in said subgroup (3), R² and R³ together with the carbonatom (C¹) to which they are attached form a saturated monocyclic (C5-C8)carbocyclic ring, such as cyclopentyl, cyclohexyl or cylcoheptyl,preferably cyclohexyl or cyclopentyl, which is substituted with 1 to 4substituents which are preferably selected from substituents (Z) asdefined later below.

In a subgroup (4) of the compound of formula (I) as defined above, R²′and R³′ together with the carbon atom (C¹′) to which they are attachedform an optionally substituted, saturated or partially unsaturated mono-or bicyclic (C4-C14) carbocyclic ring, preferably unsubstitutedsaturated monocyclic (C5-C8) carbocyclic ring, such as cyclopentyl,cyclohexyl or cylcoheptyl, preferably cyclohexyl or cyclopentyl. Alsopreferably in said subgroup (4) R²′ and R³′ together with the carbonatom (C1′) they are attached to form a saturated monocyclic (C5-C8)carbocyclic ring, such as cyclopentyl, cyclohexyl or cylcoheptyl,preferably cyclohexyl or cyclopentyl, which is substituted with 1 to 4substituents which are preferably selected from substituents (Z) asdefined later below, e.g. one substituent Z.

More preferably, in a subgroup (5a) of the compounds (I), R² and R³ and,respectively, R²′ and R³′ form carbocyclic rings as defined in formula(I), more preferably form carbocyclic rings as defined in subgroups (1)and, respectively, (2), even more preferably form carbocyclic rings asdefined in subgroups (3) and, respectively (4), which may be substitutedwith 1 to 4 substituents which are preferably selected from substituents(Z) as defined later below, e.g. one substituent Z.

In an even preferable subgroup (5b) of the compound of formula (I) asdefined above, R² and R³ together with the carbon atom (C¹) to whichthey are attached form a ring system as defined in subgroup (3) and R²′and R³′ together with the carbon atom (C¹′) to which they are attachedform a ring system as defined in subgroup (4), whereby the ring systemformed by R²′ and R³′ together with the carbon atom (C¹′) is identicalto the ring system formed by R² and R³ together with the carbon atom(C¹).

Subgroups 1 to 5b form part of embodiment (A) of the invention, i.e.where the substituents R¹ and R¹′ are as defined in formula (I) above.These subgroups can be combined with any R¹ and R¹′ substituent.

Highly preferred subgroups of embodiment (A), are the subgroup (5a) andeven more preferably subgroup (5b).

A second preferable embodiment (B) comprises a subgroup (6) of thecompound of formula (I) as defined above, wherein R¹, R², R³, R¹′, R²′and R³′ each independently is optionally substituted mono- ormulticyclic (C5-C14)aryl; optionally substituted mono- or multicyclic(C5-C14)heteroaryl; optionally substituted mono- or multicyclic(C4-C14)cycloalkyl; optionally substituted mono- or multicyclic(C4-C14)heterocyclyl; optionally substituted straight or branched chain(C1-C50)alkyl, preferably straight chain (C1-C30)alkyl; optionallysubstituted straight or branched chain, preferably straight chain,(C2-C50)alkenyl, preferably straight chain (C2-C30)alkenyl; oroptionally substituted straight or branched chain, preferably straightchain, (C2-C50)alkynyl, preferably straight chain (C2-C30)alkynyl; oroptionally substituted straight or branched chain (C1-C50)heteroalkylcomprising 1 to 4 heteroatoms selected from N, O, S or Si. Theoptionally substituted moieties as defined above contain preferably 1 to4 substituents which are preferably selected from substituents (Z) asdefined later below.

Preferable embodiments (B) of compounds (I) are any of subgroups (7) to(11), optionally in any combinations thereof:

In a subgroup (7) of the compound of formula (I) as defined above, R²,R²′, R³ and R³′ are each independently selected from unsubstitutedstraight chain (C1-C50)alkyl, preferably (C1-C30)alkyl, more preferably(C1-C20)alkyl, such as hexyl, heptyl, octyl, decyl, undecyl, docedyl,preferably decyl.

In a subgroup (8) of the compound of formula (I) as defined above, R²and R²′ each represents same radical and, respectively, R³ and R³′ eachrepresents same radical.

In a subgroup (9) of the compound of formula (I) as defined above, R²and R²′ are same and each represents methyl.

In a subgroup (10) of the compound of formula (I) as defined above, R²and R²′ are same and each represents (C6-C30)alkyl.

In a subgroup (11) of the compound of formula (I) as defined above, R³and R³′ are same and each represents (C6-C30)alkyl.

A third preferable embodiment (C) of the compounds (I) is a subgroup(12). In a subgroup (12) of the compound of formula (I) as defined aboveR¹ and R¹′ are same or different, preferably same, and each representsoptionally substituted, saturated or partially unsaturated cyclichydrocarbyl of 5 to 14 ring atoms optionally containing 1 to 4heteroring atoms selected from N, O, P, S or Si, or optionallysubstituted mono- or multicyclic (C5-C14)aryl, preferably unsubstitutedmonocyclic (C5-C7)aryl. Also preferably in said subgroup (12) R¹ and R¹′are same or different, preferably same and each represents substitutedmono- or multicyclic (C5-C14)aryl, preferably monocyclic (C5-C7)arylwhich is substituted with 1 to 4 substituents which are preferablyselected from substituents (Z) as defined later below.

A fourth preferable embodiment (D) of the compounds (I) is a subgroup(13). In a subgroup (13) of the compound of formula (I) as definedabove, R¹ and R¹′ are same or different, preferably same, and eachrepresents optionally substituted branched or straight chain, preferablyunsubstituted straight chain, (C6-C30)alkyl or methyl. This embodimentalso covers the option that R¹ and R¹′ are same or different, preferablysame, and each represents optionally substituted branched or straightchain, preferably unsubstituted straight chain, (C2-C5)alkyl.

For the avoidance of doubt it is stressed that the preferred definitionsof R¹ and R¹′ given in subgroups 12 and 13 can be combined with any ofthe preferred substituent definitions of subgroups 1 to 11 to form evenmore preferred compounds.

Further preferred compounds of formula (I) are of subgroup (14) with thefurther proviso that at least two of R¹, R² and R³, and at least two ofR¹′, R²′ and R³′, respectively, are other than H, methyl, iso-butyl ortert-butyl.

Further preferred compounds of formula (I) are of subgroup (15) with thefurther proviso that at least two of R¹, R² and R³, and at least two ofR¹′, R²′ and R³′, respectively, are other than H, methyl, ethyl,1-propyl, isopropyl, 1-butyl, iso-butyl or tert-butyl.

Further preferred compounds of formula (I) are of subgroup (16) with thefurther proviso that at least two of R¹, R² and R³, and at least two ofR¹′, R²′ and R³′, respectively, are each other than CH₃ preferably otherthan straight or branched chain saturated or partially unsaturated(C1-C3)hydrocarbyl, more preferably other than straight or branchedchain saturated or partially unsaturated (C1-C4)hydrocarbyl,

Further preferred compounds of formula (I) are of subgroup (17) with thefurther proviso that at least two of R¹, R² and R³, and at least two ofR¹′, R²′ and R³′, respectively, are preferably other than straight orbranched chain saturated or partially unsaturated (C2-C3)hydrocarbyl,more preferably other than straight or branched chain saturated orpartially unsaturated (C2-C4)hydrocarbyl.

Each of subgroups (14), (15), (16) and (17) are useful for embodimentswherein very high purity products, e.g. polymers, are desirable afterthe modification step with compound (I).

Further preferable compounds of formula (I) as defined above formsubgroup (Ia). In this subgroup R¹ and R¹′ are same or different,preferably same, and each represents optionally substituted branched orstraight chain, preferably unsubstituted straight chain, (C2-C30)alkyl,which is preferably (C6-C30)alkyl; or methyl, more preferably methyl;and

-   -   R² and R³ together with C¹ atom to which they are attached form        an optionally substituted, saturated or partially unsaturated        mono- or bicyclic (C4-C14)carbocyclic ring, preferably        optionally substituted, more preferably unsubstituted saturated        monocyclic (C5-C8)carbocyclic ring;    -   and R²′ and R³′ together with the carbon atom (C¹′) to which        they are attached form an optionally substituted, saturated or        partially unsaturated mono- or bicyclic (C4-C14)carbocyclic        ring, preferably optionally substituted, more preferably        unsubstituted saturated monocyclic (C5-C8)carbocyclic ring;        whereby the ring system formed by R² and R³ together with C¹ is        preferably identical to a ring system formed by R²′ and R³′        together with C¹′.

Any substituted moiety preferably contains 1 to 4 substituents (Z) asdefined later below, e.g. one substituent Z.

Especially preferred cyclic radicals are cyclopentyl and cyclohexyl inthis subgroup.

One of the preferred compounds of this more preferable subgroup of (Ia)is the compound of formula (Ia) which is di-(1-methylcyclohexyl)peroxide(formula Ia):

Another preferred compound is (Ia′), di(1-methylcyclopentyl)peroxide.

A second preferred subgroup (Ib) of compounds (I) is an embodiment (B)as defined above, wherein R², R²′, R³ and R³′ are as defined in subgroup(6) above, preferably as defined in subgroups (7) to (11), and R¹ andR^(1′) are according to preferable embodiment (C).

In preferable subgroup (Ib) of compounds of formula (I) as definedabove, R¹ and R¹′ are both same and represent an optionally substituted,preferably unsubstituted, monocyclic (C5-C7)aryl;

-   -   R² and R²′ are same and are both methyl; and    -   R³ and R³′ are same and are both optionally substituted branched        or straight chain (C6-C50)alkyl, more preferably unsubstituted        straight chain (C6-C30)alkyl, such as (C6-C20)alkyl.

Any substituted moiety preferably contains 1 to 4 substituents (Z) asdefined later below, e.g. one substituent Z.

One of the preferred compounds of formula (I) of this preferablesubgroup of (Ib) the compound of formula (Ib) which isDi-(1-methyl-1-phenylundecyl)peroxide (formula Ib):

Other preferred compounds of subgroup (Ib) includedi-(1-methyl-1-phenylheptyl)peroxide

A third preferred subgroup (Ic) of compounds (I) is an embodiment (B) asdefined above, wherein R², R²′, R³ and R³′ are as defined in subgroups(7), (8), (10) or (11) and R¹ and R¹′ are according to preferableembodiment (C) or (D).

In one preferable subgroup (Ic) of compounds of formula (I) as definedabove, R¹ and R¹′ are both same and represent an optionally substituted,preferably unsubstituted, monocyclic (C5-C7)aryl;

-   -   R² and R²′ are same and are both optionally substituted branched        or straight chain, preferably unsubstituted straight chain,        (C6-C50)alkyl, more preferably unsubstituted straight chain        (C6-C30)alkyl, such as (C6-C20)alkyl; and    -   R³ and R³′ are same and are both optionally substituted branched        or straight chain, preferably unsubstituted straight chain,        (C6-C50)alkyl, more preferably unsubstituted straight chain        (C6-C30)alkyl, such as (C6-C20)alkyl.

In a further preferable subgroup (Id) of compounds (I), R¹ and R¹′ areaccording to embodiment (D), preferably R¹ and R¹′ are same and are bothmethyl; and R² and R²′ are same and are both optionally substitutedbranched or straight chain, preferably unsubstituted straight chain,(C6-C50)alkyl, more preferably unsubstituted straight chain(C6-C30)alkyl, such as (C6-C20)alkyl; and R³ and R³′ are same and areboth optionally substituted branched or straight chain, preferablyunsubstituted straight chain, (C6-C50)alkyl, more preferablyunsubstituted straight chain (C6-C30)alkyl, such as (C6-C20)alkyl.

In other preferred embodiments of the invention none of R¹-R³ or R¹′-R³′represents an aromatic group.

Where one or more of R¹-R³ or R¹′-R³′ represents an aromatic radicalthis is especially preferably a phenyl group optionally substituted byone to three, such as one, group Z as hereinbefore defined.

Where one or more of R¹-R³ or R¹′-R³′ represents a cycloalkyl radicalthis is especially preferably a cyclohexyl or cyclopentyl groupoptionally substituted by one to three, such as one, group Z ashereinbefore defined.

In the compounds of formula (I) there are preferably no more than twocycloalkyl groups. In further preferred compounds there are no more thantwo cyclic groups (e.g. carbocyclic, heterocyclic or aromatic groups) inthe compound of formula (I). In a most preferred embodiment of theinvention there are two cyclic groups which each are formed by R² and R³together with C¹ and by R²′ and R³′ together with C¹′.

These preferred embodiments apply to any compound of formula (I), inparticular any compounds forming part of the sub groups above.

The optional substituents of embodiments (A), (B), (C), (D), (Ia), (Ib),(Ic) and (Id) (and any optional substituent present in the compounds ofthe invention) are preferably one to four substituents (Z) selected froma saturated or partially unsaturated (C1-C30)hydrocarbyl, a functionalgroup, a saturated or partially unsaturated (C1-C30)hydrocarbyl whichoptionally bears a functional group as defined above, or from anaromatic hydrocarbyl, which optionally bears a functional group.Preferred substituents (Z) are branched or straight chain(C1-C20)hydrocarbyl or a functional group as defined above. Preferably,no substituted radical should carry more than 1 substituent Z.

Highly preferred substituents (Z) which can be present on any optionallysubstituted moiety of the compounds of the invention include C1-6alkyls, especially methyl, ethyl, propyl or tertbutyl; C5-8 cycloalkyl;or phenyl. Where a methyl substituent carries a phenyl side group, theformed group is, of course, benzyl. Where an alkyl substituent carries acycloalkyl side group, the formed group is, of course, alkylcycloalkyl,and so on.

Where a phenyl group carries one substituent it is preferably para tothe binding to carbon atom C¹/C¹′. Where a cyclohexyl group carries onesubstituent, it is preferably beta to the C¹/C¹′ carbon atom.

Said specific compounds of formula (Ia), (Ib), (Ia′) and (Ib′) are novelas such. The invention is further directed to the compound of formula(Ia) as defined above. Thus the invention is directed to the compound offormula (Ib) as defined above. The invention is further directed to thecompound of formula (Ia′) as defined above. The invention is furtherdirected to the compound of formula (Ib′) as defined above.

The most preferred subgroups of formula (I) and of formula (V) aresubgroups Ia and Ib, even preferably subgroups (Ia) including thecompounds (Ia) and (Ia′).

Highly preferred compounds of the invention are therefore of formula(II)

wherein n 0 to 3, preferably 0 or 1 forming a cyclopentyl or cyclohexylgroup respectively, R⁴ and R⁴′ each independently represent a straightchain alkyl group having 1 to 30 carbon atoms, preferably methyl orstraight chain alkyl group having 6 to 20, preferably 6 to 12, carbonatoms, more preferably methyl, and

-   -   wherein one or preferably both ring systems independently are        unsubstituted or optionally substituted by 1 to 4 substituents Z        as defined above. It is most preferred that the ring systems are        unsubstituted.

Further highly preferred compounds of the invention are also of formula(III)

-   -   wherein Ar and Ar′ independently represent a phenyl, benzyl or        naphthyl group optionally substituted by 1 to 4 substituents Z        as defined above,    -   R⁴ and R⁴′ each are methyl; and    -   R⁵ and R⁵′ each independently represent a straight chain alkyl        group having C6-30 carbon atoms, preferably 6 to 20, more        preferably 6 to 12 carbon atoms,

Most preferred is compounds of formula (II) as defined above.

Preparation of the Compounds of Formula (I)

The compounds of the invention include novel and known compounds. Theuse of the known compounds as a free radical generating agent,preferably for modifying a polymer composition, is novel. Thus saidknown compounds may be commercially available. Alternatively, thecompounds of the invention can be prepared according to or analogouslyto known methods described in the chemical literature.

As an example, the compounds (I) as defined above can be preparedaccording to the following scheme 1 using known procedures which aredescribed in a literature and well known for a skilled person in theart.

Peroxides of formula (I) as defined above can be prepared in severalknown ways, and more specifically tertiary peroxides can be preparedfrom the corresponding tertiary alcohols under acidic conditions to givecompounds (I). The alcohols are either commercially available, or can beprepared from a suitable ketone combined with a organometallic reagent,more specifically a Grignard (RMgX, where X is an halogen) ororganolithium (RLi) reagent.

References to synthetic methods are as follows:

-   -   1) Milas, N. A., Surgenor, D. M., J. Am. Chem. Soc., 643-644,        1946    -   2) Hey, D. H., Stirling, C. J. M., Williams, G. H, J. Chem.        Soc., 1054-1058, 1957    -   3) Organic Synthesis, Smith, M. B., The McGraw-Hill Companies        Inc., 2002

Work up procedures are routine. The formed tertiary alcohol andcorresponding peroxide can be purified by removing the solvent in vacuoand purifying the residue by any of the methods known to those skilledin the art, such as crystallization.

Compounds of formula (I) can also be prepared from tertiary alcohols viaconversion to a hydroperoxide —OOH type compound. This process allowsthe preparation of asymmetrical peroxides. Thus for example, a tertiaryalcohol can be converted to a tertiary halide and reacted with hydrogenperoxide, perhaps in the presence of a promoter such as silvertrifluoroacetate and a non nucleophilic base such as sodiumhydrocarbonate to form a teriary hydroperoxide. The tertiaryhydroperoxide can then be reacted with the a tertiary bromide (perhapsthe same as used earlier in the reaction or optionally a differencetertiary bromide) to form the final diperoxide materials of formula (I).Again, a promoter such as silver trifluoroacetate/NaHCO₃ might be used.These reactions are summarised in the scheme below:

In view of the low levels of volatile decomposition products formedduring activation of the peroxides of the invention, the presentinvention reduces or minimises the fire, explosion and health risks inan working environment caused by the use of free radical generatingagents compared to the prior art.

The first group and the second of compounds of the invention as definedabove and in claim 1-3 in terms of the decomposition product(s) thereof,the third group of compounds of formula (I) of the invention as definedabove with a general formula and by means of the preferable subgroups,in any combinations, as well as in claims 4-15 below, are abbreviatedherein below as “Compound of the invention” for the sake of convenience,only. The preferred subgroup of Compound of the invention is compoundsof formula (I) including the preferable embodiments and subgroups asdefined above and in claims.

End Uses and End Applications of the Invention

I. Modification Method of Polymers

1. Crosslinking of Polymers

The below defined crosslinking step is preferable for use in thecrosslinking process of a cable of the invention as defined above and inbelow claims. Moreover said crosslinking step as such forms anindependent invention.

One preferable embodiment of said modification method of polymers iscrosslinking of polymers by radical reaction using one or more freeradical generating agents, wherein at least one said free radicalgenerating agent is Compound of the invention as defined above.

The term “crosslinking” is well known and commonly used in the polymerfield and means forming, primarily, of interpolymer crosslinks (bridges)via radical reaction.

In principle, the polymers usable in the crosslinking process of thepresent invention are not limited and can be polymers of any type.

In one preferable embodiment, said crosslinkable polymer is a polyolefinwhich can be a homopolymer of an olefin or a copolymer of an olefin withone or more comonomers.

One preferable group of crosslinkable polyolefins includes homopolymerof ethylene or copolymer of ethylene with one or more comonomers, suchas 1) a branched polyethylene homo- or copolymer produced in highpressure by radical polymerisation and well known as low densitypolyethylene (LDPE) homo or copolymer or 2) a linear polyethylene homo-or copolymer produced by low pressure polymerisation using acoordination catalyst, such as well known linear very low densitypolyethylene, linear low density polyethylene (LLDPE), medium densitypolyethylene (MDPE) or high density polyethylene (HDPE), 3)polypropylene polymers, including homopolymers and random polymers ofpolypropylene and heterophasic copolymer of propylene, or 4)polybutylene polymers, as non-limiting examples only.

One preferable group of crosslinkable ethylene polymers is 1) LDPEhomopolymer or LDPE copolymer with one or more comonomers including C3or higher alpha-olefin comonomer(s), polar comonomers and comonomerswith at least two double bonds, such as diene comonomers. High pressurepolymerisation is a well known technology in the polymer field and canbe effected in a tubular or an autoclave reactor, preferably, in atubular reactor. Further details about high pressure radicalpolymerisation are given in WO 93/08222.

In one preferable embodiment the crosslinkable LDPE is an LDPE copolymerof ethylene with a polar group containing comonomer(s) and, optionally,with other comonomer(s). As examples of comonomers having polar groupsmay be mentioned the following: (a) vinyl carboxylate esters, such asvinyl acetate and vinyl pivalate, (b) (meth)acrylates, such asmethyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate andhydroxyethyl(meth)acrylate, (c) olefinically unsaturated carboxylicacids, such as (meth)acrylic acid, maleic acid and fumaric acid, (d)(meth)acrylic acid derivatives, such as (meth)acrylonitrile and(meth)acrylic amide, and (e) vinyl ethers, such as vinyl methyl etherand vinyl phenyl ether.

Amongst these comonomers, vinyl esters of monocarboxylic acids having 1to 4 carbon atoms, such as vinyl acetate, and (meth)acrylates ofalcohols having 1 to 4 carbon atoms, such as methyl (meth)acrylate, arepreferred.

Especially preferred comonomers are butyl acrylate, ethyl acrylate andmethyl acrylate. Still more preferably, the polar copolymer comprises acopolymer of ethylene with C₁- to C₄-alkyl acrylate, such as methyl,ethyl, propyl or butyl acrylates or vinyl acetate, or any mixturethereof.

The term “(meth)acrylic acid” and “(meth)acrylate” are intended toembrace both acrylic acid and methacrylic acid and, respectively“methacrylate” and “acrylate”.

Another preferable group of crosslinkable polymers are unsaturatedpolymers, wherein the unsaturation is provided by double bonds,preferably carbon-carbon (C—C) double bonds. More preferably, saidunsaturated polymer comprises carbon-carbon double bonds, in a totalamount of carbon-carbon double bonds/1000 carbon atoms of 0.1 or more,more preferably of 0.2 or more, and most preferably more than 0.37, morepreferably at least 0.40. Preferably in this embodiment the total amountof carbon-carbon double bonds in the unsaturated polymer is of at least0.5/1000 carbon atoms. The upper limit of the amount of carbon-carbondouble bonds present in the unsaturated polymer is not limited and maypreferably be less of than 5.0/1000 carbon atoms, preferably less than3.0/1000 carbon atoms, or more preferably less than 2.5/1000 carbonatoms.

Unsaturated polymer means herein a homopolymer, wherein the unsaturationis provided by a chain transfer agent, or a copolymer, wherein theunsaturation is provided by polymerizing a monomer in the presence of atleast a polyunsaturated comonomer and optionally in the presence of achain transfer agent. Preferably, said carbon-carbon double bondspresent in the unsaturated polymer include vinyl groups, which vinylgroups originate preferably from i) a polyunsaturated comonomer, fromii) a chain transfer agent, or from iii) any mixture thereof.

Said polyunsaturated comonomer is preferably a diene, preferably a dienewhich comprises at least eight carbon atoms, the first carbon-carbondouble bond being terminal and the second carbon-carbon double bondbeing non-conjugated to the first one. Preferred dienes are selectedfrom C₈ to C₁₄ non-conjugated dienes or mixtures thereof, morepreferably selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene,1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, ormixtures thereof. Even more preferably, the diene is selected from1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, orany mixture thereof.

In addition to the vinyl groups originating from the polyunsaturatedcomonomer, the content of vinyl groups may also be originated, alone oradditionally, from a chain transfer agent which introduces vinyl groups,such as propylene.

Preferred unsaturated polyolefins are crosslinkable LDPE as definedabove which has the above C—C double bond unsaturation provided bycopolymerising ethylene in high pressure together with at least apolyunsaturated comonomer, preferably diene as defined above, and/or inthe presence of chain transfer agent as defined above. Moreover, saidcrosslinkable LDPE suitable for the present invention is preferably anLDPE copolymer which is prepared by copolymerising ethylene with atleast one polyunsaturated comonomer, preferably with at least one dieneas defined above. Such polymers are well known and described e.g. inWO93/08222, EP1695996 or WO2006/131266.

Alternatively, or in addition to the double bonds of the unsaturatedpolymer, the polymer composition of the invention may contain additives,such as known crosslinking boosters, which provide double bonds to thepolymer composition. In such case the amount of these double bonds maybe the preferable amount as given above for C—C double bonds ofunsaturated polymer, or if an unsaturated polymer is present, then theabove given preferable amounts of C—C double bonds of polymer ispreferably the total sum of the double bonds originating fromunsaturated polymer and from the double bonds originating from suchadditives.

Also linear ethylene polymers prepared using said low pressurepolymerisation are very suitable for the crosslinking of the invention.As an example VLLDPE, LLDPE, MDPE and HDPE polymers can be mentioned.They can be produced in a known manner in a single or multistageprocesses using one or more of e.g. Ziegler-Natta catalysts, single sitecatalysts, including metallocenes and non-metallocenes, andCr-catalysts. All said catalysts are very well known in the field. Themultistage process includes any combinations of polymerisationprocesses, such as slurry polymerisation, solution polymerisation, gasphase polymerisation, or any combinations thereof, in any order.

Generally, crosslinkable polymers that are usable in the presentinvention include any known polymers, e.g. commercially availablepolymers, or they can prepared in a known manner according to oranalogously to polymerisation process described in the literature.Naturally any mixtures of polymers can also be used.

The amount of the Compound of the invention as a free radical generatingagent used for the crosslinking is not critical and can vary dependingon the desired crosslinking degree and the type and characteristics ofthe crosslinkable polymer. As an example only, the amount of said freeradical generating agent of the invention may be less than 10.0 wt %,less than 6.0 wt %, less than 5.0 wt %, less than 3.5 wt %, e.g. between0.1 to 3.0 wt %, such as 0.2 to 2.6 wt %, based on the weight of thecrosslinkable polymer composition, depending i.a. on the molecularweight of Compound and the desired degree of crosslinking.

The crosslinking may be carried out in a known manner, typically inelevated temperature, such as 140° C. or more, preferably 150° C. ormore. And said step may be effected under slightly pressurisedconditions, e.g. up to 20 bar, e.g. up to about 13 bar, pressure.Typically the crosslinking temperature is at least 20° C. higher thanthe temperature used in melt mixing step of the polymer layer materialand can be estimated by a skilled person.

Using the formulation of the invention has been found to allow areduction in the pressure needed either during cross-linking, cooling orboth. In fact the use of ambient pressure may be achievable in either orboth of these steps and this forms a further aspect of the invention.

II. Polymer Composition

The below defined polymer composition is preferable for use in thecrosslinking process of a cable of the invention as defined above and inbelow claims. Moreover said polymer composition as such forms anindependent invention.

The invention thus provides also a polymer composition comprising a freeradical generating agent which is Compound of the invention as definedabove. Preferably the polymer composition comprises at least one polymercomponent and at least one free radical generating agent, which is acompound of formula (I) including the preferred embodiments andsubgroups thereof, as defined above or in claim 1 or dependent claimsthereof.

Also a process for producing a polymer composition is provided, whereinthe Compound of the invention is added to a polymer composition.

The amount of the Compound of the invention can naturally vary dependingon the desired modification method. Examples of the amounts are givene.g. above under “1. Crosslinking of polymers”. Moreover, the polymercomposition of the invention may additionally, comprise further freeradical generating agent(s), such as another Compound of the invention.

Furthermore, polymers suitable for the polymer composition of theinvention are not limited and include e.g. polymers 1) to 4),preferably 1) LDPE homo and copolymers, as described above under “1.Crosslinking of polymers”.

The polymer composition of the invention can be in a well known powderor pellet form, or in a form of polymer melt. Polymer powder of theinvention may i.a. be obtained directly from the polymerization process,optionally further processed, e.g. sieved, and/or optionally treated ormixed with further components.

The polymer pellets of the invention can be produced in a well knownmanner. In one process for forming the pellets of the invention thepolymer powder or melt obtained from a polymerization process, oralternatively polymer pellets, may optionally be mixed with othercomponents and pelletised e.g. by extrusion in a known pelletisingequipment. The Compound of the invention may be added 1) to a mixture ofa polymer composition prior to the pelletising step or 2) after thepelletising step by adding the Compound of the invention to thepreformed pellets by mixing and/or impregnating, optionally in a carriermedium, to obtain the polymer pellets of the invention.

Alternatively, Compound of the invention can added to the polymer powderor polymer pellets directly in a production line of an end product, suchas cable production line. Addition can be effected in a mixing steppreceding the end product formation step or during the end productformation step, e.g. cable extrusion step. Such addition can be effectto the polymer composition in powder or pellet form or to a melt of saidpowder or pellets which melt may optionally contain further components.

Accordingly the invention provides a polymer powder, polymer pellets ora polymer melt comprising a polymer composition and a free radicalforming agent, wherein said free radical forming agent is Compound ofthe invention.

In one preferable embodiment of the pellets or powder of the invention,said pellets or powder are in a package, such as a container includingboxes and bags. Such containers can be supplied for further use. E.g. anend producer, e.g. a cable producer, can then use the pellets of theinvention as such for polymer modification step without need to add anyfree radical generating agent.

Moreover, the polymer composition of the invention may further containother components, such as other polymers as mentioned above, oradditives, such as stabilizers.

In one preferable embodiment of the polymer composition of the inventionsaid polymer composition further comprises additives, such as one ormore of antioxidants, stabilisers, processing aids, scorch retardants,crosslinking boosters or water tree retardants, or any mixtures thereof.As antioxidant, sterically hindered or semi-hindered phenols, optionallysubstituted with functional group(s), aromatic amines, aliphaticsterically hindered amines, organic phosphates, thio compounds, andmixtures thereof, can be mentioned. Typical cross-linking boosters mayinclude compounds having a vinyl or an allyl group, e.g.triallylcyanurate, triallylisocyanurate, and di-, tri- ortetra-acrylates. As further additives, flame retardant additives, acidscavengers, fillers, such as carbon black, and voltage stabilizers canbe mentioned. All the above mentioned additives are well known inpolymer field. Such compositions are very useful for wire and cableapplications, such as for cables of the invention discussed below.

The invention further provides (a) a process for crosslinking a polymercomposition via free radical formation using one or more free radicalgenerating agents, wherein the crosslinking is effected by producingmethane as a decomposition product of said crosslinking step in anamount of less than 300 ppm (weight), when determined according to amethod as described below under “GC-analysis protocol”. Preferably saidcrosslinking step is carried out without producing methane as adecomposition product of said crosslinking step. A preferable embodimentof said process for crosslinking a polymer composition by radicalreaction using a free radical generating agent results in a crosslinkedpolymer composition and produces a CH₄ content of less than 300 ppm(weight), preferably of less than 200 ppm (weight), preferably of lessthan 100 ppm (weight), more preferably of from 0 to 50 ppm (weight) whenmeasured as defined below under “GC-analysis protocol”.

The invention provides also independently (b) a process for crosslinkinga polymer composition via free radical formation using one or more freeradical generating agents, wherein the crosslinking is carried out usinga Compound, preferably compound of formula (I), of the invention. Apreferred crosslinking process is the above process (b). In demandingend applications it is preferred that said crosslinking according toprocess (b) is carried out using a free radical generating agent whichdoes not produce methane (CH₄) during crosslinking step.

Preferably the crosslinking process is carried out under “crosslinkingconditions” which means herein under free radical agent decomposingconditions. E.g. an elevated temperature is typically used foraccelerating the decomposition of the radical and thus the crosslinkingstep. Moreover, “in the absence of CH₄ originating from said freeradical generating agent” means that the free radical generating agentdoes not result in CH₄ as a decomposition product thereof during thecrosslinking step.

The invention also provides a crosslinked polymer composition obtainableby the crosslinking process of the invention as defined above.

In a preferable embodiment of the crosslinking process and thecrosslinked polymer composition of the invention said free radicalgenerating agent is Compound of the invention.

Said crosslinking process is further defined above under “1.Crosslinking of polymers”.

III. End Applications

1. Cable

The below defined cable is preferable for use in the crosslinkingprocess of a cable of the invention as defined above and in belowclaims. Moreover said cable as such forms an independent invention.

The new principle of the invention is highly feasible in wire and cableapplications of polymers.

Accordingly, the invention further provides a cable comprising thepolymer composition of the invention as defined above and below,preferably under “II. Polymer composition”, referred herein below as“polymer composition of the invention”.

In one preferable embodiment said cable comprises a conductor surroundedwith one or more layers, wherein at least one layer comprises saidpolymer composition of the invention.

The term “conductor” means herein above and below that the conductorcomprises one or more wires. Moreover, the cable may comprise one ormore such conductors. Preferably the conductor is an electricalconductor.

In one embodiment of the cable of the invention at least one layer is aninsulation layer which comprises said polymer composition of theinvention.

In another embodiment of the cable of the invention at least one layeris a semiconductive layer comprising said polymer composition of theinvention. “Semiconductive layer” means herein that said layer comprisescarbon black and has a volume resistivity of 100 000 Ω-cm or below whenmeasured at 23° C. or 90° C., or, when measured according to ISO 3915using a plaque, has a volume resistivity of 100 Ω-cm or below at 23° C.,or of 1000 Ω-cm or below at 90° C.

In further embodiment, the cable of the invention comprises a jacketinglayer and optionally one or more layers selected from an insulationlayer and semiconductive layer surrounded by said jacketing layer,wherein said jacketing layer comprises said polymer composition of theinvention.

As one further embodiment of the cable of the invention, a low voltagecable is provided which comprises an insulation layer and optionally ajacketing layer, wherein said insulation layer comprises said polymercomposition of the invention.

As a further embodiment of the cable of the invention, a power cable isprovided which comprises at least an inner semiconductive layer,insulation layer and an outer semiconductive layer, in that order,optionally surrounded by a jacketing layer, wherein at least one of saidlayers, preferably at least the inner semiconductive layer andinsulation layer, comprises said polymer composition of the invention.

In the context of the present invention, a low voltage cable is a cableoperating in voltages 1 kV or below. A power cable is defined to be acable transferring energy operating at any voltage, typically operatingat voltages higher than 1 kV. The voltage applied to the power cable canbe alternating (AC), direct (DC), or transient (impulse). In a preferredembodiment, the power cable prepared according to the present inventionis operating at voltages higher than 6 kV and are known i.a. as mediumvoltage (MV), high voltage (HV) and extra high voltage (EHV) powercables, which terms have well known meaning and indicate the operatinglevel of such cable.

Said outer semiconductive layer of said power cable of the invention canbe non-strippable, i.e. bonded and non-peelable, or strippable, i.e.non-bonded and peelable. Said terms have well known meanings in the wireand cable field.

2. Preparation Process of a Cable

The below defined preparation process of a cable is preferable for usein the crosslinking process of a cable of the invention as defined aboveand in below claims. Moreover said preparation process of a cable assuch forms an independent invention.

A preferable embodiment of the process for preparing a cable of theinvention comprises steps of applying, preferably by (co)extrusion, oneor more layers on a conductor, which layers comprise a polymercomposition, wherein at least one layer comprises said polymercomposition of the invention.

The term “(co)extrusion” means herein that in case of two or morelayers, said layers can be extruded in separate steps, or at least twoor all of said layers can be coextruded in a same extrusion step, aswell known in the art.

In said process of the invention the components of a layer material aremixed in a separate mixer before being introduced into the extruder forproducing said layers or are added directly to an extruder and mixedtherein before forming to a layer. Additives and further components canbe added during the mixing step. The mixture in extruder is subjected toan elevated temperature, typically above the melting point of thepolymer components and then (co)extruded on a conductor in a manner verywell known in the field. E.g. conventional extruders and mixers may beused in the process of the invention.

The above described polymer powder, polymer pellets or melt of theinvention, which comprise said polymer composition of the inventioncomprising Compound of the invention, can each equally be used in saidprocess for preparing cables and they can be prepared prior their use inthe cable preparation step or they can be prepared directly in a cableproduction line during a cable manufacturing process, as described abovee.g. under “II. Polymer composition”. Accordingly, 1) preformed powderor pellets of a polymer composition of the invention comprising Compoundof the invention, may be subjected to the cable production line; or 2)said Compound of the invention may be added together with pellets orpowder to a mixing step before forming the cable layer(s). Such mixingstep can be a separate step in a separate mixing device arranged in thecable production line to precede the cable layer formation step, e.g. anextrusion step. Alternatively, Compound of the invention can be addedduring the layer formation step e.g. in an extruder, whereby it can beintroduced to the extruder together with or after the addition ofpolymer powder or polymer pellets. The addition point in an extruder isnot limited, whereby the Compound of the invention can be added at theinlet of the extruder or at a later feed point arranged along theextruder. Accordingly the addition of Compound of the invention may takeplace at the time the polymer material is in solid non-molten, partlymolten or molten state, i.e. a melt mixture. The obtained molten mixtureof a layer material is then (co)extruded on to a conductor to form acable layer. In a preferred cable preparation process of the invention alow voltage cable or, more preferably, a power cable of the invention asdefined above under 1.1. Cable is produced. The obtained cable can befurther processed for the end use application.

Typically the cable of the invention is crosslinked after the formationof cable layers. The invention further provides a process forcrosslinking a cable by radical reaction using one or more free radicalgenerating agents, comprising step of: applying one or more layerscomprising a polymer composition on a conductor, wherein at least onelayer comprises one or more free radical generating agents, crosslinkingby radical reaction said at least one layer comprising said free radicalgenerating agent(s), and recovering the crosslinked cable in aconventional manner for further use; wherein in said process saidcrosslinking is effected by producing methane as a decomposition productof said crosslinking step in an amount of less than 300 ppm (weight),when determined according to a method described below under “GC-analysisprotocol”, preferably said crosslinking step is carried out withoutproducing methane as a decomposition product of said crosslinking step.

A further independent crosslinking process for crosslinking a cable byradical reaction using one or more free radical generating agents,comprising step of: applying one or more layers comprising a polymercomposition on a conductor, wherein at least one layer comprises one ormore free radical generating agent, crosslinking by radical reactionsaid at least one layer comprising said free radical generatingagent(s), and recovering the crosslinked cable in a conventional mannerfor further use; wherein said crosslinking is carried out in thepresence of Compound of the invention as a free radical generatingagent, preferably in the presence of a compound of formula (I) asdefined above and below in claims. In another preferable embodiment thisindependent crosslinking process is dependent on the above crosslinkingprocess wherein the features are defined by means of the decompositionproducts.

In above crosslinking processes of the invention crosslinking conditionscan vary depending i.a. on the used materials and cable size. Thecrosslinking of the invention is effected e.g. in a known mannerpreferably in an elevated temperature. Preferably the lowest temperaturein a cable layer during the crosslinking step is above 140° C., morepreferably above 150° C., such as 160-210° C. The crosslinking may becarried out in a liquid or gas medium, such as in an inert gas, such asN₂, atmosphere. The pressure during the crosslinking step of theinvention is typically up to 20 bar, preferably up to 13 bar, such as10-15 bar, in inert atmosphere. Said crosslinking step of the inventionis also described above under “1. Crosslinking of polymers” and aboveunder “II. Polymer composition”.

A further preferable embodiment of the crosslinking process of theinvention comprises a further step of cooling the crosslinked cablepreferably under pressurized conditions in a cooling medium e.g. in gasor liquid, such as N₂, oil or water. The cooling is effected in acooling zone, which may be optionally integrated with the precedingcrosslinking zone, e.g. in a known vulcanization tube. As an exampleonly, continuous catenary vulcanization (CCV) tube can be mentioned. Thetemperature at the layer closest to conductor is typically below 200°C., e.g. 160-190° C., at the beginning of the cooling zone/step. Thepressure during the cooling step of the invention is typically keptabove atmospheric pressure, e.g. up to 20 bar, preferably up to 13 bar,such as 10-12 bar. The cable is removed from the pressurized coolingstep, when the temperature of the cable layers is clearly below themelting point of the polymer layer material thereof. Accordingly, thecrosslinked cable of the invention may leave the pressurized coolingstep of the invention e.g. when the temperature of the conductor of saidcable is below 110° C. depending on the layer polymer material,preferably between 70-90° C., at the exit of the pressurized coolingzone.

The crosslinking and cooling step is normally carried out underpressurized conditions to prevent the formation of voids due to volatiledecomposition products of e.g. peroxides. The process of the inventionthus enables to remove the crosslinked and cooled cable from thepressurized cooling zone in a temperature higher than in the prior art,when measured from the conductor. Also preferably, the cooling may beeffect at lower pressures compared to prior art.

Optionally, if desired, the crosslinked cable of the invention may besubjected to an additional non-pressurised cooling step after saidpressurized cooling step, for further cooling of the cable.

The cable preparation process of the invention optionally comprises afurther recovering step of the cable coming from the cooling step.Recovering may be effected by winding the cable on a cable drum in aknown manner.

In a further embodiment of the process of the invention the cableobtained from the cooling step and optionally recovered, e.g. wound to acable drum, may optionally be subjected, if needed in some applications,to a subsequent degassing step i.a. for removing or reducing anyvolatile decomposition products possibly resulting from saidcrosslinking step of the invention. In said degassing step the cable ofthe invention is preferably exposed either in ambient or elevatedtemperature for a period of time. As an example only, said degassingtemperature may be e.g. 50-80° C., and for a time period of one to fourweeks. However, due to the crosslinking process of the invention saiddegassing step may be shortened considerably or even avoided due todecreased level of said volatile by-products.

The cable of the invention produced by the above process of theinvention may be further processed, e.g. protected with a protectivelayer, and/or optionally covered by a jacketing layer in a subsequentfinishing step in a known manner and recovered for the end use thereof.

The invention thus provides also a crosslinked cable comprisingcrosslinked polymer composition as defined above, preferably acrosslinked low voltage cable or power cable, more preferably acrosslinked power cable, as defined above. Preferably said crosslinkedcable is obtainable by any of the crosslinking processes as definedabove.

In one embodiment of a crosslinking process of the invention acrosslinked power cable is produced which is selected from a crosslinkedMV cable, wherein the lowest degree of crosslinking in a cable layer(s)meets the requirements as specified in IEC 60502, or a crosslinked HVcable, wherein the lowest degree of crosslinking in a cable layer(s)meets the requirements as specified in IEC 60840, which specificationsare well known in the W&C field.

The advantageous Compounds of the invention are preferable free radicalgenerating agents which can be used for improving the quality of theproducts, e.g. in cable production processes. Due to the presentinvention the amount of voids in polymer products, such as cable layerscan be reduced or even avoided, since less or no volatile decompositionproducts are formed from e.g. when Compound of the invention is used formodifying the polymer. Moreover, the invention also enables to improvethe processability of a cable, i.a. in terms of safer and fasterprocessing. E.g. the crosslinking process of the invention can be fasterand/or more economical, since both cooling and/or degassing steps may becarried out in a reduced time and/or in a less energy consuming manner,if desired.

Determination Methods

Unless otherwise stated the below determination methods were used todetermine the properties defined generally in the description part andclaims and in the experimental part.

Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and isindicated in g/10 min. The MFR is an indication of the flowability, andhence the processability, of the polymer. The higher the melt flow rate,the lower the viscosity of the polymer. The MFR is determined at 190° C.for polyethylenes and may be determined at different loadings such as2.16 kg (MFR₂) or 21.6 kg (MFR₂₁). The MFR is determined at 230° C. forpolypropylenes.

Density

The density was measured according to ISO 1183D. The sample preparationwas executed according to ISO 1872-2.

Gel Content

The gel content was determined according to ASTM D 2765-01, method Ausing a crosslinked sample which consists of the polymer compositionunder test and prepared according to “Preparation of samples,crosslinking” below.

Gel content on a cable is carried out using ASTM D 2765-01 method B.

Methods A and B give comparable results.

GC-Analysis Protocol

In definitions of the Compounds, Polymer compositions, cables andpreparation process and modification methods thereof as defined aboveand in claims below, the volatile, e.g. CH₄, content given in ppm(weight) or as “absent” is determined by gas chromatography (GC) from asample which is modified, e.g. crosslinked.

The test is used to determine the produced volatiles, e.g. methane,content of a free radical generating agent. The test free radicalgenerating agent is used in such an amount with which a crosslinkingdegree expressed as gel content of 50% was achieved, preferably gelcontent of at least 50%. Crosslinking conditions of the sample are notcritical and may be effected e.g. as described below under

“Preparation of Samples, Crosslinking”

Volatiles are measured by taking a sample specimen of 1 g with athickness of 1.5 mm from a modified, e.g. crosslinked composition, e.g.a plaque or cable. In the case of a cable comprising a crosslinkedlayer(s), the sample specimen is taken from a layer material of acrosslinked and cooled cable sample that is taken at the exit of acrosslinking/cooling zone, such as at the exit of a vulcanisation tube,after pressurised cooling step in a manner known for a skilled person.

The collection of volatiles from said sample specimen (to a head spacebottle, see below) is started within one hour after the modificationstep is stopped, or in case of a crosslinked and cooled cable, withinone hour after the cable sample is taken at the exit of acrosslinking/cooling zone.

A sample specimen of a thickness of 1.5 mm and of a weight of 1 g is cutfrom the middle of a plaque which is 100 mm wide and 100 mm long. Theobtained sample (specimen) is placed in a 120 ml head space bottle withan aluminium crimp cup with seal and heat treated at 60° C. for 1.5 hfor collecting any gaseous volatiles present in said sample. Then0.3-0.5 ml of the gas captured in the sample bottle is injected into agas chromatograph, wherein the presence and content of the volatiles,e.g. methane, which are desired to be measured in a known manner. Doublesamples are analysed and a “zero-sample” without free radical generatingagent/modification is used as a reference. The instrument used hereinwas a Varian 3400 with a Al₂O₃/Na₂SO₄-column of 0.53 mm×50m, supplied byChrompack.

Specimen from a Cable

A sample specimen of a thickness of 1.5 mm and of a weight of 1 g is cutin an axial direction from said cable sample from the middle distance(in radial direction) of the polymer layer(s) ring surrounding theconductor of said cable sample (i.e. at the distance of ½ radius of saidcable layer ring). The collection and determination of volatiles wascarried out as described above.

Specimen from a Plaque

The volatile, e.g. CH₄, content given in ppm (weight) or as “absent” isdetermined by gas chromatography (GC) from a sample plaque which ismodified, e.g. crosslinked according to the protocol described in thesection entitled “Preparation of samples, crosslinking” above. The testcomposition contains 2 parts test peroxide and 100 parts test polymer(i.e. sufficient to cause a degree of cross-linking of 50% or more).

A sample specimen of a thickness of 1.5 mm and of a weight of 1 g is cutfrom the middle of a plaque which is 100 mm wide and 100 mm long. Thecollection and determination of volatiles was carried out as describedabove.

Materials

In each test for references and for examples of this application thetest arrangement for the reference polymer, i.e. the polymer without anyadded additive such as organic peroxide, and for the testedcompositions, i.e. the reference polymer containing the organicperoxide, was the same.

The unsaturated polymer: The polymer is a poly(ethyleneco-1,7-octadiene)

Poly(ethylene co-1,7-octadiene) Manufacture

Ethylene was compressed in a 5-stage precompressor and a 2-stage hypercompressor with intermediate cooling to reach an initial reactionpressure of ca. 2950 bar. The total compressor throughput was ca. 30tons/hour. In the compressor area approximately 120 kg propylene/hourwas added as chain transfer agent to maintain an MFR of 3.2 g/10 min.Here also 1,7-octadiene was added to the reactor in amount of ca. 50kg/h. The compressed mixture was heated to approximately 165° C. in apreheating section of a front feed three-zone tubular reactor with aninner diameter of ca. 40 mm and a total length of ca. 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerization reaction to reach peaktemperature of ca. 280° C. after which it was cooled to approx 250° C.The subsequent 2nd and 3rd peak reaction temperatures were ca. 280° C.and ca. 270° C., respectively, with a cooling in between down toapproximately 250° C. The reaction mixture was depressurized by a kickvalve, cooled and polymer was separated from unreacted gas.

The obtained polymer had a total number of C—C carbon double bonds of1.286/1000 C and the number of vinyl groups was 0.994 vinyl groups/1000C. The density of the material was 920 kg/m³ and MFR (2.16 kg)=3.2 g/10min.

The above unsaturated polymer was used in testing the examples of theinvention containing compounds (I) of the invention as the crosslinkingagent, comparative examples with dicumulperoxide as the crosslinkingagent and the reference example containing no crosslinking agent.

The commercial reference organic peroxide, dicumyl peroxide, wassupplied by AkzoNobel.

Preparation of Samples, Impregnation

The test polyethylene pellets were ground to a fine powder in a Retschgrinder with a 1.5 mm sieve. The powder obtained was impregnated withthe test peroxide dissolved in a pentane solution until the pentane hadevaporated to give a dry powder of the test peroxide and the testpolymer. The content of the test composition was 3 parts test peroxideand 100 parts test polymer when the gel content of the crosslinked testcomposition was tested as described below. The content of the testcomposition was 2 parts test peroxide and 100 parts test polymer whenthe volatiles content was determined as described in the GC-analysisprotocol.

Preparation of Samples, Crosslinking

The test plaques had the following dimensions and crosslinking cycle.The plaques were 100 mm long, 100 mm wide, and 0.1 mm thick when usedfor determination of the gel content as described below, and 100 mmlong, 100 mm wide, and 1.5 mm thick when the volatiles content wasdetermined as described in the GC-analysis protocol below. Thecrosslinking was conducted in a Specac press, where the composition waskept at 120° C. for 1 min at 5 bar, then the temperature was increasedwith 60° C./min for 1 min to reach 180° C. at 5 bar, and kept at 180° C.at 5 bar for 12 min, followed by cooling to ambient temperature over 30min at 5 bar.

EXAMPLES Example 1 Preparation of Di-(1-methyl-1-phenylundecyl)peroxide

(R¹, R¹′=phenyl; R², R²′=methyl; R³, R³′=decyl)

A. 1-methyl-1-phenylundecyl alcohol

To a suspension of 2.43 g (0.1 mol) magnesium turnings in 10 ml ofdiethyl ether was added 0.1 ml of 1,2-dibromoethane and the mixture wasstirred. 22.17 g (0.1 mol) of 1-bromodecane in 20 ml diethyl ether wasadded dropwise and the mixture was refluxed for 15 minutes, then cooled.9.61 g (0.08 mol) of acetophenone in 20 ml diethyl ether was added whilecooling on ice bath. The ice bath was removed and the reaction mixturestirred at room temperature for 30 minutes. The mixture was then pouredinto a slurry of 30 g ammonium chloride in 150 ml water and 100 g icewhile stirring vigorously. The mixture was filtered, the ether layerseparated and the aqueous layer extracted twice with 50 ml of ether. Theorganic layers were combined, washed with water, 10% NaHSO₃, brine,dried and evaporated to give 22.48 g of clear oil. The oil was purifiedwith dry column chromatography using pentane. The eluant was evaporatedgiving 17.22 g (82%) of 1-methyl-1-phenylundecyl alcohol as a viscouscolorless oil.

B. 1-methyl-1-phenylundecyl hydroperoxide

10.50 g (0.04 mol) of 1-methyl-1-phenylundecyl alcohol was dissolved in50 ml of dichloromethane, cooled in ice bath, 10.6 ml (12.29 g, 0.08mol) of trimethylsilyl bromide was added and the mixture stirred for 1 hunder protection from moisture. The solution was diluted with 100 mlether and washed four times with 50 ml water, brine, dried andevaporated to give crude 2-phenyl-2-bromododecane. 35 ml of 2.3 Mhydrogen peroxide in THF (0.08 mol) was added to the 2-phenyl-2-dodecylbromide and the mixture was cooled on ice bath. 8.84 g (0.04 mol) ofsilver trifluoroacetate was added. 70 ml of conc. NaHCO₃ was added andthe mixture filtered. The reaction flask and the filter cake was rinsedwith diethyl ether. The aqueous phase was separated and the organicphase washed with conc. NaHCO₃, 50 ml water, brine, dried and evaporatedto give an oil. The oil was purified by flash chromatography using 2:8ether:pentane as eluent. The yield of 1-methyl-1-phenylundecylhydroperoxide was 30%.

C. Di-(1-methyl-1-phenylundecyl)peroxide

0.942 g (3.6 mmol) of 1-methyl-1-phenylundecyl alcohol was dissolved in5 ml of dichloromethane, 1 ml of trimethylsilyl bromide (7.2 mmol) wasadded and the mixture stirred for 1 h under protection from moisture.The solution was diluted with 15 ml of diethyl ether, washed with water(3×10 ml), 15 ml brine, dried and evaporated to give 1.18 of crude2-phenyl-2-bromododecane. 795 mg of silver trifluoroacetate (3.6 mmol)was dissolved in 5 ml THF. To the crude bromide was added 500 mg of1-methyl-1-phenylundecyl hydroperoxide (1.8 mmol) dissolved in 10 mlTHF. This mixture was cooled in ice-salt bath to −15° C. and the silvertrifluoroacetate solution added with a pipette. 2 ml of brine was thenadded, followed by 10 ml conc. NaHCO₃. The reaction mixture was stirredand filtered. The reaction flask and the filter cake were rinsed with 15ml diethyl ether. The aqueous phase was separated and the organic phasewashed with conc. NaHCO₃, 15 ml water, 15 ml brine, dried and evaporatedto give 1.40 g of a yellowish oil. Purification was done using a 1:9ether:pentane mixture as eluent. The yield was 409 mg (43%). ¹³C-NMR(CDCl₃) δ 14.33, 22.91, 23.96, 24.06, 24.19, 29.55, 29.72, 29.82, 30.24,32.13, 40.68, 40.97, 84.18, 126.16, 126.69, 127.86, 145.59, 145.71

Example 2 Preparation of Di(1-methyl-cyclohexyl)peroxide

(R¹=methyl; R²+R³ Form Together with C¹ a Cyclohexyl Ring andR^(1′)=Methyl; R^(2′)+R^(3′) Form Together with C^(1′) a CyclohexylRing)

A. Di(1-methyl-cyclohexyl)peroxide

1-methylcyclohexanol (30 g, 0.26 mol) was placed in a 100 mL threenecked round bottomed flask and was stirred. The flask was cooled in abrine/ice bath, dropping funnel fitted and fitted with a static N₂supply. The dropping funnel was charged with 98% sulfuric acid (16.14ml) and water (6.45 ml) giving a 70% sulfuric acid solution. This wasadded dropwise to the 1-methylcyclohexanol and stirring continued togive a viscous brown mixture. The bath was recharged with ice/brine,dropping funnel rinsed with water and recharged with 35% hydrogenperoxide (6.98 mL, 0.125 mol) and added dropwise. The solution separatedinto two phases. Cyclohexanol (150 mL) was added and the mixture wastransferred to a separating funnel. The aqueous fraction was extractedwith another portion of cyclohexane (150 ml) and the combined organicfractions washed with 1M NaOH (2×100 mL), water (2×150 mL), dried andevaporated to give a viscous colourless oil. (12.98 g). The oil wassorbed onto silica gel then placed on a silica gel column and elutedwith cyclohexane. After evaporation at reduced pressure 0.7 g colourlessoil of di(1-methyl-cyclohexyl)peroxide was obtained. ¹³C-NMR (CDCl₃) δ22.45, 25.01, 25.95, 35.39, 78.58

Example 3 Preparation of Di(1-methyl-cyclopentyl)peroxide

(R¹=Methyl; R²+R³ Form Together with C¹ a Cyclopentyl Ring andR^(1′)=Methyl; R^(2′)+R^(3′) Form Together with C^(1′) a CyclopentylRing)

A. Di(1-methyl-cyclopentyl)peroxide

A 250 ml tri-neck round bottom flask was equipped and a 50 ml additionfunnel and the flask was cooled <0 C. 30 g of 1-methylcyclopentanol (0.3M, 1 EQ) was added to the flask. 70% H₂SO₄ solution was prepared andcooled in an ice bath. The H₂SO₄ (12.71 ml, 0.91 M, 3 EQ) was added dropwise over 15 minutes and the reaction mixture was stirred for ˜2.5 hoursin order to allow all the 1-methylcyclopentanol to dissolve. With thereaction stirring, 8.11 ml of H₂O₂ 35% (wt) (0.24 M, 0.8 EQ) was addeddrop wise over 15 minutes. The reaction was left stirring overnight. Thereaction mixture was transferred to a separation funnel and extractedthree times with 50 ml of pentane each time. Organic layers werecollected and the aqueous was set aside. The organic layers wereextracted 3 times with 50 ml of 1N NaOH each time to remove excess acid.The organic layer was collected, dried and concentrated. The residue waspurified by chromatography on a silica column using pentane as themobile phase. The product fractions were concentrated to yield 973 mg ofdi(1-methyl-cyclopentyl)peroxide as a colorless oil. ¹³C-NMR (CDCl₃) δ24.43, 24.75, 37.13, 89.23

Gel Content

The gel content of the LDPE copolymer prepared as described above wasdetermined according to the method above and the results are shown below(Table 1.)

TABLE 1 Gel content Example Gel content (%) Reference polymer 0 withoutperoxide Ib 51 Ia 62 Ia′ 82GC-Analysis

GC-analysis was performed to evaluate the amount of formed CH₄. Theexample is compared to a sample using dicumyl peroxide, which representthe conventional solution used today. The results are presented below(Table 2).

TABLE 2 GC-analysis of the CH₄ content. Example CH₄ content (ppm)Dicumyl peroxide 719 (gel content 93%) Ia′  <5* (gel content 84%)* *atvalues less than 5 ppm the amount of methane is so small that noisemasks an accurate reading. Value less than 5 ppm are considered torepresent no methane formed therefore.Preparation of a Crosslinked Cable of the Invention:

A power cable comprising an inner semiconductive layer, an insulationlayer and an outer semiconductive layer for experimental testing isprepared by coextruding on a conductor said layers in given order usinga conventional extruder line and conventional extrusion conditions.

The layer materials are conventional polymer grades and each layercomprises a peroxide compound of the invention as a crosslinking agent.

The semiconductive material used in the cable, both as inner and outersemicon, is a poly(ethylene-co-butylacrylate) polymer (with abutylacrylate content of 17 wt %) containing 40 wt % of a furnace black.The composition is stabilised with an antioxidant of the polyquinolinetype and contains 1 wt % of the peroxide of the invention as acrosslinking agent.

The middle insulation layer is formed of low density polyethylene LDPE(MFR₂=2 g/10 min) containing 2 wt-% of the peroxide of the invention and0.2 wt-% of 4,4′-thiobis(2-tert.-butyl-5-methylphenol).

The obtained cable is immediately after extrusion subjected to aconventional vulcanisation tube and crosslinked in a known manner usingwell known crosslinking conditions. After crosslinking the cable is thencooled in cooling zone of said vulcanisation tube at a desired pressureand temperature. The cooling step is stopped when the desiredtemperature measured from the conductor is achieved. Typically thecooling step can be effected in a lower pressure and/or the cooling stepcan be stopped in a higher temperature at conductor compared tocorresponding cable crosslinked to a same gel content, but usingdicumylperoxide as the crosslinking agent. The crosslinked and cooledlayer is wound to a cable drum and transferred to a degassing step toremove the volatile(s) content, if any. This step can typically be donein a lower temperature and/or a shorter period compared to correspondingcable crosslinked to a same gel content, but using dicumylperoxide asthe crosslinking agent.

I claim:
 1. A process for preparing a crosslinked cable, comprising: applying one or more layers comprising a polymer composition on a conductor, wherein at least one layer comprises one or more free radical generating agents, so as to form an uncrosslinked cable; crosslinking by radical reaction said at least one layer comprising said one or more free radical generating agents to obtain a crosslinked cable; cooling the obtained crosslinked cable under pressurized conditions; and reducing or removing the content of volatile decomposition products(s), at ambient or in elevated temperature, from said crosslinked cable obtained from said cooling step, characterized in that said process comprises one or two of the following features (i) or (ii): (i) said reduction or removal step is carried out in more than 50% shorter period of time than the time period required for a reference cable which is a crosslinked and cooled cable having the same structure and layer material in each of said one or more layers, and prepared using the same process steps and conditions thereof, as well as the same degree of crosslinking, as said claimed crosslinked and cooled cable, but using a dicumyl peroxide as the free radical generating agent, in order for said reference cable to obtain the same content of said volatile decomposition product(s) as said claimed cable by using the same reduction or removal conditions as said claimed cable; or (ii) said reduction or removal step is carried out in a lower temperature than the temperature required for a reference cable which is a crosslinked and cooled cable having the same structure and layer material in each of said one or more layers, and prepared using the same process steps and conditions thereof, as well as the same degree of crosslinking, as said claimed crosslinked and cooled cable, but using a dicumyl peroxide as the free radical generating agent, in order for said reference cable to obtain the same content of said volatile decomposition product(s) as said claimed cable.
 2. A process for preparing a crosslinked cable, comprising the steps of: (i) applying one or more layers comprising a polymer composition on a conductor, wherein at least one layer comprises one or more free radical generating agents; (ii) crosslinking by radical reaction said at least one layer comprising said one or more free radical generating agents; (iii) cooling the obtained crosslinked cable under pressurized conditions; and (iv) reducing or removing the content of volatile decomposition products(s), at ambient or in elevated temperature, from said crosslinked cable obtained from said cooling step; wherein said one or more free radical generating agents is a compound of formula (I)

wherein R¹ and R¹′ are each independently H, substituted or unsubstituted saturated or partially unsaturated hydrocarbyl; or substituted or unsubstituted aromatic hydrocarbyl; wherein each of said substituted or unsubstituted saturated or partially unsaturated hydrocarbyl or aromatic hydrocarbyl optionally comprises one or more heteroatoms; and wherein said substituted saturated or partially unsaturated hydrocarbyl or substituted aromatic hydrocarbyl comprises independently 1 to 4 substituents selected from a functional group; saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; or aromatic hydrocarbyl optionally bearing a functional group; R², R²′, R³ and R³′ are each independently H, substituted or unsubstituted saturated or partially unsaturated hydrocarbyl; or substituted or unsubstituted aromatic hydrocarbyl; wherein each of said substituted or unsubstituted saturated or partially unsaturated hydrocarbyl or aromatic hydrocarbyl optionally comprises one or more heteroatoms; and wherein said substituted saturated or partially unsaturated hydrocarbyl or substituted aromatic hydrocarbyl comprises independently 1 to 4 substituents selected from a functional group; a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; or an aromatic hydrocarbyl optionally bearing a functional group; or R² and R³ together with the carbon atom (C¹) to which they are attached form an unsubstituted or substituted, saturated or partially unsaturated carbocyclic ring moiety of 3 to 14 C-atoms; unsubstituted or substituted saturated or partially unsaturated heteroring moiety of 3 to 14 ring atoms comprising 1 to 6 heteroatoms selected from O, N, P, S or Si; or unsubstituted or substituted aromatic ring moiety of 3 to 14 C-atoms optionally comprising 1 to 4 heteroatoms; wherein said carbocyclic ring, heteroring or aromatic ring system is optionally fused with another ring system having 4 to 14 ring atoms; and wherein said substituted carbocyclic ring, heteroring or aromatic ring system comprises 1 to 4 substituents selected independently from a functional group, saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; or an aromatic hydrocarbyl optionally bearing a functional group; or R²′ and R³′ together with the carbon atom (C¹′) to which they are attached form an unsubstituted or substituted saturated or partially unsaturated carbocyclic ring moiety of 3 to 14 C-atoms; unsubstituted or substituted saturated or partially unsaturated heteroring moiety of 3 to 14 ring atoms comprising 1 to 6 heteroatoms selected from O, N, P, S or Si; or unsubstituted or substituted aromatic ring moiety of 3 to 14 C-atoms optionally comprising 1 to 4 heteroatoms; wherein said carbocyclic ring, heteroring or aromatic ring system is optionally fused with another ring system having 4 to 14 ring atoms; and wherein said substituted carbocyclic ring, heteroring or aromatic ring system comprises 1 to 4 substituents selected independently from a functional group, a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; or an aromatic hydrocarbyl optionally bearing a functional group; or R² and R²′ form together a bivalent substituted or unsubstituted saturated or partly unsaturated hydrocarbyl optionally containing 1 to 4 heteroatoms, wherein R² is linked to C^(I) and R²′ to C¹′, respectively, forming together with —C¹—O —O —C ¹′— a substituted or unsubstituted saturated or partially unsaturated carbocyclic ring moiety of 3 to 14 C-atoms comprising optionally, in addition to said at least two O atoms, 1 to 4 further heteroatoms; wherein said carbocyclic ring or heteroring system is optionally fused with another ring system having 4-14 ring atoms; or functional derivatives thereof; with a proviso that at least two of R¹, R² and R³, and at least two of R¹′, R²′ and R³′, respectively, are other than H or methyl.
 3. The process as claimed in claim 1, wherein compound for use as a free radical generating agent bears one or more moieties in its structure which are decomposable to a decomposition product in a free radical generating step, characterized in that said compound is selected from one or more of: a compound, wherein said one or more decomposable moieties result in a CH₄ content of less than 300 ppm (weight), preferably of less than 200 ppm (weight), preferably of less than 100 ppm (weight), more preferably of 0 to 50 ppm (weight), when determined according to a method as described in the description under “GC-analysis protocol”; or a compound without any such moiety that is decomposable to CH₄ as said decomposition product; or any mixture thereof.
 4. The process as defined in claim 1, wherein said reduction or removal step is carried out in more than 70%, preferably in more than 90%, shorter period of time than the reduction or removal step of the crosslinked and cooled reference cable as defined in claim
 1. 5. The process of claim 1, wherein the crosslinked and cooled cable is further subjected to one or more optional steps selected from: a non-pressurized cooling step, wherein the crosslinked and cooled cable is further cooled in a cooling medium, a recovering step after the pressurized cooling step and before the reduction or removal step, wherein the crosslinked and cooled cable is collected, preferably wound to a cable drum, and/or a finishing step, wherein the obtained crosslinked cable is finished in a conventional manner for further use.
 6. The process as defined in claim 1 for preparing a crosslinked cable which comprises at least an insulation layer, wherein said at least insulation layer is crosslinked in the presence of said free radical generating agent.
 7. The process as defined in claim 1 for preparing a crosslinked cable which comprises at least one semiconductive layer, wherein said at least one semiconductive layer is crosslinked in the presence of said free radical generating agent.
 8. The process as defined in claim 1 for preparing a crosslinked cable which comprises a jacketing layer and optionally one or more layers selected from an insulation layer and semiconductive layer surrounded by said jacketing layer, wherein at least said jacketing layer is crosslinked in the presence of said free radical generating agent.
 9. The process as defined in claim 1 for preparing a crosslinked cable which is selected from any of the following cables: a low voltage cable comprising a conductor surrounded by an insulation layer and optionally a jacketing layer, wherein said insulation layer is crosslinked in the presence of said free radical generating agent; or a power cable comprising an electrical conductor surrounded by one or more layers comprising at least an inner semiconductive layer, insulation layer and an outer semiconductive layer, in that order, and optionally surrounded by a jacketing layer, wherein at least one of said layers, preferably at least inner semiconductive layer and insulation layer, is crosslinked in the presence of said free radical generating agent.
 10. The process as defined in claim 1, wherein during the crosslinking and cooling step of the invention no detectable methane is formed when measured as defined in description under “GC-analysis protocol” and thus the crosslinking method may be made without a degassing step.
 11. The process as claimed in claim 1 wherein the free radical generating agent is a compound of formula (I) as defined in claim
 2. 12. The process as claimed in claim 2 wherein in said compound of formula (I), R² and R³ together with carbon atom (C¹) to which they are attached form an optionally substituted carbocyclic ring moiety of 3 to 12 ring C-atoms or an optionally substituted heteroring moiety of 3 to 12 ring atoms containing 1 to 6, preferably 1 to 4, heteroatoms selected from O, N, P, S or Si, and wherein said carbocyclic or heterocyclic ring system is optionally fused with another ring system having 4 to 14 ring atoms, preferably R² and R³ together with carbon atom (C¹) form a (C3-C12) carbocyclic ring moiety.
 13. The process as claimed in claim 2 wherein in said compound of formula (I) R²′ and R³′ together with carbon atom (C¹′) to which they are attached form an optionally substituted carbocyclic ring moiety of 3 to 12 ring C-atoms or an optionally substituted heteroring moiety of 3 to 12 ring atoms containing 1 to 6, preferably 1 to 4, heteroatoms selected from O, N, P, S or Si, and wherein said carbocyclic or heterocyclic ring system is optionally fused with another ring system having 4 to 14 ring atoms, preferably R²′ and R³′ together with carbon atom (C¹′) form a (C3-C12) carbocyclic ring moiety;
 14. The process as claimed in claim 2 wherein in said compound of formula (I) the ring system formed by R²′ and R³′ together with the carbon atom (C¹′) to which they are attached is same as the ring system formed by R² and R³ together with the carbon atom (C¹) to which they are attached; and wherein R¹and R^(h)each represents optionally substituted branched or straight chain, preferably unsubstituted straight chain, (C6-C30)alkyl or methyl, preferably wherein R¹ and R¹′ are identical.
 15. The process as claimed in claim 2 wherein in said compound of formula (I) R² and R³ together with carbon atom (C¹) to which they are attached form an optionally substituted carbocyclic ring moiety of 3 to 12 ring C-atoms which is optionally fused with another ring system having 4 to 14 ring atoms, and wherein R²′ and R³′ together with carbon atom (C″) to which they are attached form an optionally substituted carbocyclic ring moiety of 3 to 12 ring C-atoms which is optionally fused with another ring system having 4 to 14 ring atoms, and wherein the ring system formed by R²′ and R³′ together with the carbon atom (C¹′) to which they are attached is the same as the ring system formed by R² and R³ together with the carbon atom (C¹) to which they are attached; and wherein R¹and R¹′ each represents optionally substituted branched or straight chain, preferably unsubstituted straight chain, (C6-C30)alkyl or methyl.
 16. The A process as claimed in claim 2 wherein in said compound of formula (I) R¹and R¹are same or different, preferably same, and each represents optionally substituted branched or straight chain, preferably unsubstituted straight chain, (C2-C 30)alkyl, which is preferably (C6-C30)alkyl; or methyl, more preferably methyl; and R² and R³ together with C¹atom to which they are attached form an optionally substituted, saturated or partially unsaturated mono- or bicyclic (C4-C14)carbocyclic ring, preferably unsubstituted saturated monocyclic (C5-C8)carbocyclic ring; and R²′ and R³′ together with the carbon atom (C¹′) to which they are attached form an optionally substituted, saturated or partially unsaturated mono- or bicyclic (C4-C14)carbocyclic ring, preferably unsubstituted saturated monocyclic (C5-C8)carbocyclic ring; whereby the ring system formed by R² and R³ together with C¹is preferably identical to a ring system formed by R²′ and R³′ together with C¹′.
 17. The process as claimed in claim 2 wherein in said compound of formula (I) R¹, R², R³, R¹′, R²′ and R³′ each independently is optionally substituted mono- or multicyclic (C5-C14)aryl; optionally substituted mono- or multicyclic (C5-C 14)heteroaryl; optionally substituted mono- or multicyclic (C4-C14)cycloalkyl; optionally substituted mono- or multicyclic (C4-C14)heterocyclyl; optionally substituted straight or branched chain (C1-050)alkyl, preferably optionally substituted straight chain (C1-C30)alkyl; optionally substituted straight or branched chain (C1-050)alkenyl or optionally substituted straight or branched chain (C1-050)alkynyl, preferably straight chain (C1-C30)alkenyl or straight chain (C1-C30)alkynyl; optionally substituted straight or branched chain (C1-C 50)heteroalkyl comprising 1 to 4 heteroatoms selected from 0, N, P, S or Si.
 18. The process as claimed in claim 17 wherein in said compound of formula (I) R², R²′, R³ and R³′ are independently selected from unsubstituted straight chain (C1-C50)alkyl, preferably (C1-C30)alkyl, more preferably (C1-C20)alkyl, more preferably from C1-C12alkyl, more preferably from methyl or (C6-C12)alkyl.
 19. The process as claimed in claim 17 wherein in said compound of formula (I) R² and R²′ are same and each represents methyl; or R² and R²′ are same and each represents (C6-C30)alkyl.
 20. The process as claimed in claim 17 wherein in said compound of formula (I), R³ and R³′ are same and each represents (C6-C30)alkyl.
 21. The process as claimed in claim 17 wherein in said compound of formula (I) R¹ and R¹′ are both same and represent an optionally substituted, preferably unsubstituted, monocyclic (C5-C7)aryl; R² and R²′ are same and are both methyl; and R³ and R³′ are same and are both optionally substituted branched or straight chain (C6- C50)alkyl, more preferably unsubstituted straight chain (C6-C30)alkyl, such as (C6-C20)alkyl.
 22. The process as claimed in claim 21 wherein said compound is of formula (III)

wherein Ar and Ar' independently represent a phenyl, benzyl or naphthyl group optionally substituted by 1 to 4 substituents, R⁴ and R⁴′ each are methyl; and R⁵ and R⁵′ each independently represent a straight chain alkyl group having C6-30 carbon atoms, preferably 6 to 20, more preferably 6 to 12, carbon atoms.
 23. The process as claimed in claim 2 wherein in said compound of formula (I) R² and R²′ are the same radical and, R³ and R³′ are the same radical.
 24. The process as claimed in claim 3 wherein in said compound of formula (I), R′ and R^(h) are same or different, preferably same, and each represents optionally substituted, saturated or partially unsaturated cyclic hydrocarbyl of 5 to 14 ring atoms optionally containing 1 to 4 heteroring atoms selected from N, O, P, S or Si; or optionally substituted mono- or multicyclic (C5-C14)aryl, preferably unsubstituted monocyclic (C5-C7)aryl; or R¹ and R¹ ′ are same or different, preferably same, and each represents optionally substituted branched or straight chain, preferably unsubstituted straight chain, (C6-C30)alkyl or methyl.
 25. The process as claimed in claim 2 wherein in said compound of formula (I) R¹ and R¹ ′ are same and each represents methyl; and R² and R³ together with C¹ atom to which they are attached form an optionally substituted, saturated or partially unsaturated mono- or bicyclic (C4-C14)carbocyclic ring, preferably unsubstituted saturated monocyclic (C5-C8)carbocyclic ring; and R²′ and R³′ together with the carbon atom (C¹ ′) to which they are attached form an optionally substituted, saturated or partially unsaturated mono- or bicyclic (C4-C14)carbocyclic ring, preferably unsubstituted saturated monocyclic (C5-C8)carbocyclic ring; whereby the ring system formed by R² and R³ together with C^(I) is preferably identical to a ring system formed by R²′ and R³′ together with C¹′.
 26. The process as claimed in claim 25 wherein said compound is of formula (II)

wherein n is 0 to 3, and R⁴ and R⁴′ each independently represent a straight chain alkyl group having 1 to 30 carbon atoms, preferably methyl or straight chain alkyl group having 6 to 20, preferably 6 to 12, carbon atoms, more preferably methyl, and wherein one or both ring systems independently are unsubstituted or optionally substituted by 1 to 4 substituents.
 27. The process as claimed in claim 2 wherein in said compound of formula (I) said optional substitutents are each independently selected from —OH, —NR₂, wherein each R is independently H or (C1-C12)alkyl, COR″, wherein R″ is i. a. H, (C1-C 12)alkyl or —NR₂, wherein each R is as defined for —NR₂, COOR″, wherein R is as defined for —COR″; halogen, such as —F, —C1 or —I; or alkoxy, saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; or aromatic hydrocarbyl optionally bearing a functional group.
 28. The process as claimed in claim 2 wherein in said compound of formula (I) is of formula (V)

wherein the compounds are selected from any of the alternatives (i) to (iii): (i) R¹ and R¹′ are each independently H, substituted or unsubstituted saturated or partially unsaturated hydrocarbyl; wherein each of said substituted or unsubstituted saturated or partially unsaturated hydrocarbyl optionally comprises one or more heteroatoms; wherein said substituted or unsubstituted saturated or partially unsaturated hydrocarbyl include (i) straight or branched chain saturated or partially unsaturated hydrocarbyls, (ii) straight or branched chain saturated or partially unsaturated hydrocarbyls which bear saturated or partially unsaturated cyclic hydrocarbyl and (iii) saturated or partially unsaturated cyclic hydrocarbyls; wherein each of said saturated or partially unsaturated cyclic hydrocarbyl is independently a monocyclic or multicyclic ring system; and wherein said substituted saturated or partially unsaturated hydrocarbyl comprise independently 1 to 4 substituents selected from a functional group, a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group or aromatic hydrocarbyl optionally bearing a functional group; and R², R²′, R³and R³′ are each independently as defined above for R¹ and R¹′; or (ii) R¹and R¹ are each independently an optionally substituted, preferably unsubstituted, monocyclic (C5-C7)aryl, preferably phenyl, wherein said substituted monocyclic (C5-C7)aryl comprises independently 1 to 4substituents selected from a functional group, a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group or aromatic hydrocarbyl optionally bearing a functional group; and R² and R²′ are same and are both methyl; and R³ and R³′ are each independently H, substituted or unsubstituted saturated or partially unsaturated hydrocarbyl as defined above under (i) for R¹and R¹′; or (iii) R¹and R¹′ are each independently H, substituted or unsubstituted saturated or partially unsaturated hydrocarbyl as defined above under (i) for R¹and R¹′; and -R² and R³ together with the carbon atom (C¹) to which they are attached form an unsubstituted or substituted saturated or partially unsaturated carbocyclic ring moiety of 3 to 14 C-atoms, preferably of 5 to 12 C atoms; or an unsubstituted or substituted saturated or partially unsaturated heteroring moiety of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4 heteroatoms, selected from O, N, P, S or Si; wherein said carbocyclic ring or heteroring is optionally fused with another optionally substituted ring system having 4 to 14 ring atoms; and wherein said substituted carbocyclic ring or heteroring system comprises 1 to 4 substituents selected independently from a functional group, or a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group; and R²′ and R³′ together with the carbon atom (C¹′) to which they are attached form an unsubstituted or substituted saturated or partially unsaturated carbocyclic ring moiety of 3 to 14 C-atoms, preferably of 5 to 12 C atoms; an unsubstituted or substituted saturated or partially unsaturated heteroring moiety of 3 to 14 ring atoms comprising 1 to 6, preferably 1 to 4 heteroatoms, selected from O, N, P, S or Si; wherein said carbocyclic ring or heteroring system is optionally fused with another optionally substituted ring system having 4 to 14 ring atoms; and wherein said substituted carbocyclic ring or heteroring system comprises 1 to 4 substituents selected independently from a functional group or a saturated or partially unsaturated hydrocarbyl optionally bearing a functional group, with a proviso for alternatives (i) to (iii) that at least two of R′, R² and R³, and at least two of R¹′, R²′ and R³′, respectively, are other than H or methyl.
 29. The process as claimed in claim 22 wherein in said compound of formula (V) the substituents R′, R², R³, R¹′, R²′ and R³′, in alternatives (i) to (iii) are as defined in any of the preceding claims 5 to 21 respectively to said alternatives (i) to (iii).
 30. The process as claimed in claim 2 wherein the compound of formula (I) is selected from any of Di(1-methylcyclopentyl) peroxide Di-(1-methyl-l-phenylundecyl) peroxide Di-(1-methyl-1-phenylheptyl) peroxide or Di(1-methyl-cyclohexyl) peroxide.
 31. A crosslinked cable obtainable by a process as defined in claim 1, preferably a crosslinked low voltage cable or a crosslinked power cable.
 32. A compound of formula (I) as defined in claim 2, wherein R² and R³ together with carbon atom (C¹) to which they are attached and/or wherein R²′ and R³′ together with carbon atom (C¹″) to which they are attached form an optionally substituted, saturated or partially unsaturated mono- or bicyclic (C4-C14) carbocyclic ring, more preferably an optionally substituted, saturated monocyclic (C5-C8)carbocyclic ring. 